Difference between pages "BTRFS Fun" and "Help:Funtoo Editing Guidelines"

(Difference between pages)
 
(Displaying Source Code)
 
Line 1: Line 1:
{{Article}}
+
'''Thanks for your interest in contributing to the the Funtoo wiki!'''
{{fancyimportant|BTRFS is still '''experimental''' even with latest Linux kernels (3.4-rc at date of writing) so be prepared to lose some data sooner or later or hit a severe issue/regressions/"itchy" bugs. Subliminal message: '''Do not put critical data on BTRFS partitions'''.}}
+
__NOTOC__
+
=== Types of Edits ===
  
= Introduction =
+
Before we get started, let's review what changes are okay to make, and what changes are not okay:
  
BTRFS is an advanced filesystem mostly contributed by Sun/Oracle whose origins take place in 2007. A good summary is given in
+
{{TableStart}}
[http://lwn.net/Articles/342892/]. BTRFS aims to provide a modern answer for making storage more flexible and efficient. According to its main contributor, Chris Mason, the goal was "to let Linux scale for the storage that will be available. Scaling is not just about addressing the storage but also means being able to administer and to manage it with a clean interface that lets people see what's being used and makes it more reliable." (Ref. [http://en.wikipedia.org/wiki/Btrfs http://en.wikipedia.org/wiki/Btrfs]).
+
<tr class="active"><th>Type of Change</th><th>Okay?</th></tr>
 +
<tr><td>Grammar/spelling fixes</td><td>Yes</td></tr>
 +
<tr><td>New wiki content</td><td>Yes</td></tr>
 +
<tr><td>New package information</td><td>Yes</td></tr>
 +
<tr><td>Adding to existing article</td><td>Maybe -- see below</td></tr>
 +
<tr><td>Adding missing/incomplete information</td><td>Yes</td></tr>
 +
<tr><td>Making corrections</td><td>Yes</td></tr>
 +
<tr class="danger"><td>Adding work-arounds to problems experienced</td><td>No - open bug first on [http://bugs.funtoo.org bug tracker].</td></tr>
 +
{{TableEnd}}
  
Btrfs, often compared to ZFS, is offering some interesting features like:
+
{{important|Note that if you experience some problem with Funtoo Linux, during installation or otherwise, the proper course of action is to not add a work-around to our documentation, but to ''open a bug on our bug tracker.'' This is important because the problem you experienced may be a legitimate bug and the solution may be to fix the bug rather than add a work-around to our documentation. We may end up fixing a bug, making a documentation fix, or possibly both.}}
  
* Using very few fixed location metadata, thus allowing an existing ext2/ext3 filesystem to be "upgraded" in-place to BTRFS.
+
=== Basics ===
* Operations are transactional
+
* Online volume defragmentation (online filesystem check is on the radar but is not yet implemented).
+
* Built-in storage pool capabilities (no need for LVM)
+
* Built-in RAID capabilities (both for the data and filesystem metadata). RAID-5/6 is planned for 3.5 kernels
+
* Capabilities to grow/shrink the volume
+
* Subvolumes and snapshots (extremely powerful, you can "rollback" to a previous filesystem state as if nothing had happened).
+
* Copy-On-Write
+
* Usage of B-Trees to store the internal filesystem structures (B-Trees are known to have a logarithmic growth in depth, thus making them more efficient when scanning)
+
  
= Requirements =
+
Here is a list of basic wiki information that you will need to know to get started:
  
A recent Linux kernel (BTRFS metadata format evolves from time to time and mounting using a recent Linux kernel can make the BTRFS volume unreadable with an older kernel revision, e.g. Linux 2.6.31 vs Linux 2.6.30). You must also use sys-fs/btrfs-progs (0.19 or better use -9999 which points to the git repository).
+
* First, to perform edits on the wiki, you must {{CreateAccount}} and log in.
 +
* You can create a new page by navigating to http://www.funtoo.org/New_Page_Name. Underscores are the equivalent of spaces. Then select "Create" under the "Actions" menu.
 +
* Whether creating a new page or editing an existing page by clicking "Edit", you will be presented with Web-based text editor that allows you to modify the ''wikitext'' of the page. The wikitext is rendered to produce the document you see when you view the page normally.
 +
* Another fun thing you can do is click on your name under the "Account" menu once you have logged in. This will bring you to your "User" page. Then click "Create with Form" unde the "Actions" menu and enter your geographic and other information. This will allow you to be displayed on our [[Usermap]] and will also allow your full name to be displayed on [[:Category:Ebuilds|Ebuild pages]] for which you are an author. It's generally a good idea to do this.
  
= Playing with BTRFS storage pool capabilities =
+
{{tip|The following sections document how to use wikitext and Funtoo templates on the Funtoo wiki.}}
  
Whereas it would possible to use btrfs just as you are used to under a non-LVM system, it shines in using its built-in storage pool capabilities. Tired of playing with LVM ? :-) Good news: you do not need it anymore with btrfs.
+
=== Paragraphs ===
  
== Setting up a storage pool ==
+
To create a new paragraph, insert a blank line between two lines of text. If a blank line doesn't exist between two lines of wikitext, they will be combined into a single flowing paragraph.
  
BTRFS terminology is a bit confusing.  If you already have used another 'advanced' filesystem like ZFS or some mechanism like LVM, it's good to know that there are many correlations.  In the BTRFS world, the word ''volume'' corresponds to a storage ''pool'' (ZFS) or a ''volume group'' (LVM). Ref. [http://www.rkeene.org/projects/info/wiki.cgi/165 http://www.rkeene.org/projects/info/wiki.cgi/165]
+
If you leave leading whitespace at the beginning of a line, MediaWiki will render it as pre-formatted text. Beware of this. Here's an example:
  
The test bench uses disk images through loopback devices. Of course, in a real world case, you will use local drives or units though a SAN. To start with, 5 devices of 1 GiB are allocated:
+
foobar
  
<console>
+
This can rear its ugly head when specifying template parameters, so you will get this:
###i## dd if=/dev/zero of=/tmp/btrfs-vol0.img bs=1G count=1
+
###i## dd if=/dev/zero of=/tmp/btrfs-vol1.img bs=1G count=1
+
###i## dd if=/dev/zero of=/tmp/btrfs-vol2.img bs=1G count=1
+
###i## dd if=/dev/zero of=/tmp/btrfs-vol3.img bs=1G count=1
+
###i## dd if=/dev/zero of=/tmp/btrfs-vol4.img bs=1G count=1
+
</console>
+
  
Then attached:
+
{{note| ugh!}}
  
<console>
+
...instead of this:
###i## losetup /dev/loop0 /tmp/btrfs-vol0.img
+
###i## losetup /dev/loop1 /tmp/btrfs-vol1.img
+
###i## losetup /dev/loop2 /tmp/btrfs-vol2.img
+
###i## losetup /dev/loop3 /tmp/btrfs-vol3.img
+
###i## losetup /dev/loop4 /tmp/btrfs-vol4.img
+
</console>
+
  
== Creating the initial volume (pool) ==
+
{{note|This looks much better!}}
  
BTRFS uses different strategies to store data and for the filesystem metadata (ref. [https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices]).
+
=== Page and Section Capitalization ===
  
By default the behavior is:
+
In general, capitalize all words in page names and section heading except:
* metadata is '''replicated''' on all of the devices.  If a single device is used the metadata is duplicated inside this single device (useful in case of corruption or bad sector, there is a higher chance that one of the two copies is clean). To tell btrfs to maintain a single copy of the metadata, just use ''single''. Remember: '''dead metadata = dead volume with no chance of recovery.'''
+
* Articles: a, an, the
* data is '''spread''' amongst all of the devices (this means no redundancy; any data block left on a defective device will be inaccessible)
+
* Coordinating Conjunctions: and, but, or, for, nor, etc.
 +
* Prepositions (fewer than five letters): on, at, to, from, by, etc.
  
To create a BTRFS volume made of multiple devices with default options, use:
+
=== Document Hierarchy ===
  
<console>
+
Use section headings to create a document hierarchy for your page. These will define the table of contents that appears at the top of the wiki page. Create chapters, sections and sub-sections as follows:
###i## mkfs.btrfs /dev/loop0 /dev/loop1 /dev/loop2
+
</console>
+
  
To create a BTRFS volume made of a single device with a single copy of the metadata (dangerous!), use:
+
<pre>= Page Title =
  
<console>
+
== Chapter Title ==
###i## mkfs.btrfs -m single /dev/loop0
+
</console>
+
  
To create a BTRFS volume made of multiple devices with metadata spread amongst all of the devices, use:
+
=== Section Title ===
  
<console>
+
==== SubSection Title ====
###i## mkfs.btrfs -m raid0 /dev/loop0 /dev/loop1 /dev/loop2
+
</console>
+
  
To create a BTRFS volume made of multiple devices, with metadata spread amongst all of the devices and data mirrored on all of the devices (you probably don't want this in a real setup), use:
 
 
<console>
 
###i## mkfs.btrfs -m raid0 -d raid1 /dev/loop0 /dev/loop1 /dev/loop2
 
</console>
 
 
To create a fully redundant BTRFS volume (data and metadata mirrored amongst all of the devices), use:
 
 
<console>
 
###i## mkfs.btrfs -d raid1 /dev/loop0 /dev/loop1 /dev/loop2
 
</console>
 
 
{{Fancynote|Technically you can use anything as a physical volume: you can have a volume composed of 2 local hard drives, 3 USB keys, 1 loopback device pointing to a file on a NFS share and 3 logical devices accessed through your SAN (you would be an idiot, but you can, nevertheless). Having different physical volume sizes would lead to issues, but it works :-).}}
 
 
== Checking the initial volume ==
 
 
To verify the devices of which BTRFS volume is composed, just use '''btrfs-show ''device'' ''' (old style) or '''btrfs filesystem show ''device'' ''' (new style). You need to specify one of the devices (the metadata has been designed to keep a track of the what device is linked what other device). If the initial volume was set up like this:
 
 
<console>
 
###i## mkfs.btrfs /dev/loop0 /dev/loop1 /dev/loop2
 
 
WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
 
WARNING! - see http://btrfs.wiki.kernel.org before using
 
 
adding device /dev/loop1 id 2
 
adding device /dev/loop2 id 3
 
fs created label (null) on /dev/loop0
 
        nodesize 4096 leafsize 4096 sectorsize 4096 size 3.00GB
 
Btrfs Btrfs v0.19
 
</console>
 
 
It can be checked with one of these commands (They are equivalent):
 
 
<console>
 
###i## btrfs filesystem show /dev/loop0
 
###i## btrfs filesystem show /dev/loop1
 
###i## btrfs filesystem show /dev/loop2
 
</console>
 
 
The result is the same for all commands:
 
 
<pre>
 
Label: none  uuid: 0a774d9c-b250-420e-9484-b8f982818c09
 
        Total devices 3 FS bytes used 28.00KB
 
        devid    3 size 1.00GB used 263.94MB path /dev/loop2
 
        devid    1 size 1.00GB used 275.94MB path /dev/loop0
 
        devid    2 size 1.00GB used 110.38MB path /dev/loop1
 
 
</pre>
 
</pre>
  
To show all of the volumes that are present:
+
{{Note|By default, Table of Contents is disabled on the Funtoo wiki. If you would like to enable the TOC, you can place a <code><nowiki>__TOC__</nowiki></code> on a blank line where you'd like the Table of Contents to appear, or place <code><nowiki>__FORCETOC__</nowiki></code> on a blank line anywhere in the wikitext to force the TOC to appear at the top of the page.}}
  
<console>
+
In general, when creating new documents, it's best to use level-3 (three "="'s) Section Titles to break up content. Level-2 Section Titles are best used for major sections of larger documents. Use them infrequently. Level-1 Section Titles generally do not need to be used.
###i## btrfs filesystem show
+
Label: none  uuid: 0a774d9c-b250-420e-9484-b8f982818c09
+
        Total devices 3 FS bytes used 28.00KB
+
        devid    3 size 1.00GB used 263.94MB path /dev/loop2
+
        devid    1 size 1.00GB used 275.94MB path /dev/loop0
+
        devid    2 size 1.00GB used 110.38MB path /dev/loop1
+
  
Label: none  uuid: 1701af39-8ea3-4463-8a77-ec75c59e716a
+
=== Links ===
        Total devices 1 FS bytes used 944.40GB
+
        devid    1 size 1.42TB used 1.04TB path /dev/sda2
+
  
Label: none  uuid: 01178c43-7392-425e-8acf-3ed16ab48813
+
Internal links to other wiki pages can be specified as <tt><nowiki>[[pagename]]</nowiki></tt>. To specify an alternate name for the link, use <tt><nowiki>[[pagename|my link name]]</nowiki></tt>.
        Total devices 1 FS bytes used 180.14GB
+
        devid    1 size 406.02GB used 338.54GB path /dev/sda4
+
</console>
+
  
{{Fancywarning|BTRFS wiki mentions that '''btrfs device scan''' should be performed, consequence of not doing the incantation? Volume not seen?}}
+
For external links, use <tt><nowiki>[http://funtoo.org my link]</nowiki></tt> to specify a URL. If you want the URL to appear in the wikitext, you can specify it without brackets: http://forums.funtoo.org.
  
== Mounting the initial volume ==
+
=== Lists ===
  
BTRFS volumes can be mounted like any other filesystem. The cool stuff at the top on the sundae is that the design of the BTRFS metadata makes it possible to use any of the volume devices. The following commands are equivalent:
+
MediaWiki supports a number of list formats:
  
<console>
+
* Unordered List
###i## mount /dev/loop0 /mnt
+
* Unordered Item 2
###i## mount /dev/loop1 /mnt
+
** Unordered sub-item
###i## mount /dev/loop2 /mnt
+
</console>
+
  
For every physical device used for mounting the BTRFS volume <tt>df -h</tt> reports the same (in all cases 3 GiB of "free" space is reported):
+
# Ordered List
 +
# Ordered Item 2
 +
## Ordered sub-item
  
<console>
+
;Term: This is called a "definition list". It is used when defining various terms.
###i## df -h
+
Filesystem      Size  Used Avail Use% Mounted on
+
/dev/loop1      3.0G  56K  1.8G  1% /mnt
+
</console>
+
  
The following command prints very useful information (like how the BTRFS volume has been created):
+
If you need to quote a portion of text from another site, use <tt><nowiki><blockquote></nowiki></tt> as follows:
<console>
+
###i## btrfs filesystem df /mnt     
+
Data, RAID0: total=409.50MB, used=0.00
+
Data: total=8.00MB, used=0.00
+
System, RAID1: total=8.00MB, used=4.00KB
+
System: total=4.00MB, used=0.00
+
Metadata, RAID1: total=204.75MB, used=28.00KB
+
Metadata: total=8.00MB, used=0.00
+
</console>
+
By the way, as you can see, for the btrfs command the mount point should be specified, not one of the physical devices.
+
  
== Shrinking the volume ==
+
<blockquote>
 +
Wikipedia (ˌwɪkɨˈpiːdiə/ or wɪkiˈpiːdiə/ wik-i-pee-dee-ə) is a collaboratively edited, multilingual, free-access, free content Internet encyclopedia that is supported and hosted by the non-profit Wikimedia Foundation. Volunteers worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including over 4.5 million in the English Wikipedia. Anyone who can access the site can edit almost any of its articles, which on the Internet comprise[4] the largest and most popular general reference work.[5][6][7][8][9] In February 2014, The New York Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google, the largest with 1.2 billion unique visitors."[10]
 +
</blockquote>
  
A common practice in system administration is to leave some head space, instead of using the whole capacity of a storage pool (just in case). With btrfs one can easily shrink volumes. Let's shrink the volume a bit (about 25%):
+
=== Literal Text and HTML Symbols ===
  
<console>
+
Here is wikitext for the section above, which I am displaying by placing the literal wikitext between a &#60;pre&#62; and &#60;/pre&#62; tag. If you want to disable wikitext processing for an inline span of text, use &#60;nowiki&#62; and &#60;/nowiki&#62;. If you want to print out a tag literally, use &amp;#60; and &amp;#62; (In the wikitext, I used &amp;amp;#60; and &amp;amp;#62 to display these!)
###i## btrfs filesystem resize -500m /mnt
+
###i## dh -h
+
/dev/loop1      2.6G  56K  1.8G  1% /mnt
+
</console>
+
 
+
And yes, it is an on-line resize, there is no need to umount/shrink/mount. So no downtimes! :-) However, a BTRFS volume requires a minimal size... if the shrink is too aggressive the volume won't be resized:
+
  
<console>
+
<pre>
###i## btrfs filesystem resize -1g /mnt 
+
* Unordered List
Resize '/mnt' of '-1g'
+
* Unordered Item 2
ERROR: unable to resize '/mnt'
+
** Unordered sub-item
</console>
+
  
== Growing the volume ==
+
# Ordered List
 +
# Ordered Item 2
 +
## Ordered sub-item
  
This is the opposite operation, you can make a BTRFS grow to reach a particular size (e.g. 150 more megabytes):
+
;Term: This is called a "definition list". It is used when defining various terms.
  
<console>
+
If you need to quote a portion of text from another site, use <tt><nowiki><blockquote></nowiki></tt> as follows:
###i## btrfs filesystem resize +150m /mnt
+
Resize '/mnt' of '+150m'
+
###i## dh -h
+
/dev/loop1      2.7G  56K  1.8G  1% /mnt
+
</console>
+
  
You can also take an ''"all you can eat"'' approach via the '''max''' option, meaning all of the possible space will be used for the volume:
+
<blockquote>
 +
Wikipedia (ˌwɪkɨˈpiːdiə/ or wɪkiˈpiːdiə/ wik-i-pee-dee-ə) is a collaboratively edited, multilingual, free-access,
 +
free content Internet encyclopedia that is supported and hosted by the non-profit Wikimedia Foundation. Volunteers
 +
worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including over 4.5 million in the
 +
English Wikipedia. Anyone who can access the site can edit almost any of its articles, which on the Internet
 +
comprise[4] the largest and most popular general reference work.[5][6][7][8][9] In February 2014, The New York
 +
Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views
 +
and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google,
 +
the largest with 1.2 billion unique visitors."[10]
 +
</blockquote>
 +
</pre>
  
<console>
+
=== Linking to Packages ===
###i## btrfs filesystem resize max /mnt
+
Resize '/mnt' of 'max'
+
###i## dh -h
+
/dev/loop1      3.0G  56K  1.8G  1% /mnt
+
</console>
+
  
== Adding a new device to the BTRFS volume ==
+
To link to a package page, use the <code>Package</code> template:
  
To add a new device to the volume:
+
<pre><nowiki>
 +
{{Package|sys-apps/portage}}
 +
</nowiki></pre>
  
<console>
+
This template will create a link to the official wiki page for sys-apps/portage, and render using the official "English" page name, as follows:
###i## btrfs device add /dev/loop4 /mnt
+
oxygen ~ # btrfs filesystem show /dev/loop4
+
Label: none  uuid: 0a774d9c-b250-420e-9484-b8f982818c09
+
        Total devices 4 FS bytes used 28.00KB
+
        devid    3 size 1.00GB used 263.94MB path /dev/loop2
+
        devid    4 size 1.00GB used 0.00 path /dev/loop4
+
        devid    1 size 1.00GB used 275.94MB path /dev/loop0
+
        devid    2 size 1.00GB used 110.38MB path /dev/loop1
+
</console>
+
  
Again, no need to umount the volume first as adding a device is an on-line operation (the device has no space used yet hence the '0.00'). The operation is not finished as we must tell btrfs to prepare the new device (i.e. rebalance/mirror the metadata and the data between all devices):
+
{{Package|sys-apps/portage}}
  
<console>
+
If you specify a yet-to-be-documented ebuild, it will render like this (which is okay -- it will encourage people to document it):
###i## btrfs filesystem balance /mnt
+
###i## btrfs filesystem show /dev/loop4
+
Label: none  uuid: 0a774d9c-b250-420e-9484-b8f982818c09
+
        Total devices 4 FS bytes used 28.00KB
+
        devid    3 size 1.00GB used 110.38MB path /dev/loop2
+
        devid    4 size 1.00GB used 366.38MB path /dev/loop4
+
        devid    1 size 1.00GB used 378.38MB path /dev/loop0
+
        devid    2 size 1.00GB used 110.38MB path /dev/loop1
+
</console>
+
  
{{Fancynote|Depending on the sizes and what is in the volume a balancing operation could take several minutes or hours.}}
+
{{Package|sys-foo/undocumented-ebuild}}
  
== Removing a device from the BTRFS volume ==
+
=== Tables ===
  
<console>
+
Instead of using traditional MediaWiki table wikitext, use the following format:
###i## btrfs device delete /dev/loop2 /mnt
+
###i## btrfs filesystem show /dev/loop0 
+
Label: none  uuid: 0a774d9c-b250-420e-9484-b8f982818c09
+
        Total devices 4 FS bytes used 28.00KB
+
        devid    4 size 1.00GB used 264.00MB path /dev/loop4
+
        devid    1 size 1.00GB used 268.00MB path /dev/loop0
+
        devid    2 size 1.00GB used 0.00 path /dev/loop1
+
        *** Some devices missing
+
###i## df -h
+
Filesystem      Size  Used Avail Use% Mounted on
+
/dev/loop1      3.0G  56K  1.5G  1% /mnt
+
</console>
+
  
Here again, removing a device is totally dynamic and can be done as an on-line operation! Note that when a device is removed, its content is transparently redistributed among the other devices.
+
<pre>
 +
{{TableStart}}
 +
<tr class="info"><th>Header 1</th><th>Header 2</th></tr>
 +
<tr><td>Value 1</td><td>Value 2</td></tr>
 +
<tr><td>Value 3</td><td>Value 4</td></tr>
 +
{{TableEnd}}
 +
</pre>
  
Obvious points:
+
This wil render as follows:
* '''** DO NOT UNPLUG THE DEVICE BEFORE THE END OF THE OPERATION, DATA LOSS WILL RESULT**'''
+
* If you have used raid0 in either metadata or data at the BTRFS volume creation you will end in a unusable volume if one of the the devices fails before being properly removed from the volume as some stripes will be lost.
+
  
Once you add a new device to the BTRFS volume as a replacement for a removed one, you can cleanup the references to the missing device:
+
{{TableStart}}
 +
<tr class="info"><th>Header 1</th><th>Header 2</th></tr>
 +
<tr><td>Value 1</td><td>Value 2</td></tr>
 +
<tr><td>Value 3</td><td>Value 4</td></tr>
 +
{{TableEnd}}
  
<console>
+
{{tip|This table syntax has an added benefit of creating a responsive table that renders properly on mobile devices.}}
###i## btrfs device delete missing
+
</console>
+
  
== Using a BTRFS volume in degraded mode ==
+
It is possible to use the following CSS classes with <code>tr</code> (rows) and <code>td/th</code> elements to color them as desired:
 
+
{{fancywarning|It is not possible to use a volume in degraded mode if raid0 has been used for data/metadata and the device had not been properly removed with '''btrfs device delete''' (some stripes will be missing). The situation is even worse if RAID0 is used for the the metadata: trying to mount a BTRFS volume in read/write mode while not all the devices are accessible '''will simply kill the remaining metadata, hence making the BTRFS volume totally unusable'''... you have been warned! :-)}}
+
 
+
If you use raid1 or raid10 for data AND metadata and you have a usable submirror accessible (consisting of 1 drive in case of RAID1 or the two drive of the same RAID0 array in case of RAID10), you can mount the array in degraded mode in the case of some devices are missing (e.g. dead SAN link or dead drive) :
+
 
+
<console>
+
###i## mount -o degraded /dev/loop0 /mnt
+
</console>  
+
 
+
If you use RAID0 (and have one of your drives inaccessible) the metadata or RAID10 but not enough drives are on-line to even get a degraded mode possible, btrfs will refuse to mount the volume:
+
 
+
<console>
+
###i## mount /dev/loop0 /mnt
+
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
+
      missing codepage or helper program, or other error
+
      In some cases useful info is found in syslog - try
+
      dmesg | tail  or so
+
</console>
+
 
+
The situation is no better if you have used RAID1 for the metadata and RAID0 for the data, you can mount the drive in degraded mode but you will encounter problems while accessing your files:
+
 
+
<console>
+
###i## cp /mnt/test.dat /tmp
+
cp: reading `/mnt/test.dat': Input/output error
+
cp: failed to extend `/tmp/test.dat': Input/output error
+
</console>
+
  
= Playing with subvolumes and snapshots =
+
{{TableStart}}
 +
<tr class="active"><td>Class Name</td></tr>
 +
<tr class="success"><td>success</td></tr>
 +
<tr class="info"><td>info</td></tr>
 +
<tr class="warning"><td>warning</td></tr>
 +
<tr class="active"><td>active</td></tr>
 +
<tr class="danger"><td>danger</td></tr>
 +
{{TableEnd}}
  
== A story of boxes.... ==
+
=== Displaying Source Code ===
  
When you think about subvolumes in BTRFS, think about boxes. Each one of those can contain items and other smaller boxes ("sub-boxes") which in turn can also contains items and boxes (sub-sub-boxes) and so on. Each box and items has a number and a name, except for the top level box, which has only a number (zero). Now imagine that all of the boxes are semi-opaque: you can see what they contain if you are outside the box but you can't see outside when you are inside the box. Thus, depending on the box you are in you can view either all of the items and sub-boxes (top level box) or only a part of them (any other box but the top level one). To give you a better idea of this somewhat abstract explanation let's illustrate a bit:
+
To display source code, use can use the file template, specifying a <tt>lang=</tt> parameter:
  
 
<pre>
 
<pre>
(0) --+-> Item A (1)
+
{{file|name=foobar|lang=python|desc=foobarosity|body=
      |
+
import system
      +-> Item B (2)
+
}}
      |
+
      +-> Sub-box 1 (3) --+-> Item C (4)
+
      |                   |
+
      |                  +-> Sub-sub-box 1.1 (5) --+-> Item D (6)
+
      |                  |                        |
+
      |                  |                        +-> Item E (7)
+
      |                  |                        |
+
      |                  |                        +-> Sub-Sub-sub-box 1.1.1 (8) ---> Item F (9)
+
      |                  +-> Item F (10)
+
      |
+
      +-> Sub-box 2 (11) --> Item G (12)                   
+
 
</pre>
 
</pre>
  
What you see in the hierarchy depends on where you are (note that the top level box numbered 0 doesn't have a name, you will see why later). So:
+
This will produce:
* If you are in the node named top box (numbered 0) you see everything, i.e. things numbered 1 to 12
+
* If you are in "Sub-sub-box 1.1" (numbered 5), you see only things 6 to 9
+
* If you are in "Sub-box 2" (numbered 11), you only see what is numbered 12
+
  
Did you notice? We have two items named 'F' (respectively numbered 9 and 10). This is not a typographic error, this is just to illustrate the fact that every item lives its own peaceful existence in its own box. Although they have the same name, 9 and 10 are two distinct and unrelated objects (of course it is impossible to have two objects named 'F' in the same box, even they would be numbered differently).
+
{{file|name=foobar|lang=python|desc=foobarosity|body=
 +
import system
 +
}}
  
== ... applied to BTRFS! (or, "What is a volume/subvolume?") ==
+
The parameters {{c|name}} (filename), {{c|lang}} (language for syntax highlighting) and {{c|desc}} (Description, appearing as a caption) are optional. For a list of supported languages, see [http://www.mediawiki.org/wiki/Extension:SyntaxHighlight_GeSHi#Supported_languages this list].
  
BTRFS subvolumes work in the exact same manner, with some nuances:
 
  
* First, imagine a frame that surrounds the whole hierarchy (represented in dots below). This is your BTRFS '''volume'''. A bit abstract at first glance, but BTRFS volumes have no tangible existence, they are just an ''aggregation'' of devices tagged as being clustered together (that fellowship is created when you invoke '''mkfs.btrfs''' or '''btrfs device add''').
+
{{important|If you need to display the pipe ("{{!}}") character within the body of a file template, replace each "{{!}}" with <nowiki>{{!}}</nowiki> -- otherwise your file contents will not display properly. This is necessary because <nowiki>{{file}}</nowiki> is a template and the "{{!}}" character is used as a delimiter for arguments to the template.}}
* Second, the first level of hierarchy contains '''only''' a single box numbered zero which can never be destroyed (because everything it contains would also be destroyed).  
+
  
If in our analogy of a nested boxes structure we used the word '''"box"''', in the real BTRFS word we use the word '''"subvolume"''' (box => subvolume). Like in our boxes analogy, all subvolumes hold a unique number greater than zero and a name, with the exception of root subvolume located at the very first level of the hierarchy which is ''always'' numbered zero and has no name (BTRFS tools destroy subvolumes by their name not their number so '''no name = no possible destruction'''.  This is a totally intentional architectural choice, not a flaw). 
+
=== Displaying Text File Contents ===
  
Here is a typical hierarchy:
+
For displaying the contents of non-programming language text files (like config files), you have two options. You can enclose your lines within <tt>&#60;pre&#62;</tt> tags, or use the new [[Template:File|file template]]. The file template is used like so:
  
 
<pre>
 
<pre>
.....BTRFS Volume................................................................................................................................
+
{{file|name=/etc/foo.conf|desc=My foo.conf file|body=
.
+
# /etc/host.conf:
.  Root subvolume (0) --+-> Subvolume SV1 (258) ---> Directory D1 --+-> File F1
+
# $Header: /var/cvsroot/gentoo/src/patchsets/glibc/extra/etc/host.conf,v 1.1 2006/09/29
.                      |                                           |
+
}}
.                       |                                           +-> File F2
+
.                       |
+
.                       +-> Directory D1 --+-> File F1
+
.                       |                  |
+
.                       |                  +-> File F2
+
.                      |                  |
+
.                      |                  +-> File F3
+
.                      |                  |
+
.                      |                  +-> Directory D11 ---> File F4
+
.                      +-> File F1
+
.                      |
+
.                      +-> Subvolume SV2 (259) --+-> Subvolume SV21 (260)
+
.                                                |
+
.                                                +-> Subvolume SV22 (261) --+-> Directory D2 ---> File F4
+
.                                                                            |
+
.                                                                            +-> Directory D3 --+-> Subvolume SV221 (262) ---> File F5
+
.                                                                            |                  |
+
.                                                                            |                  +-> File F6
+
.                                                                            |                  |
+
.                                                                            |                  +-> File F7
+
.                                                                            |
+
.                                                                            +-> File F8
+
.
+
.....................................................................................................................................
+
 
</pre>
 
</pre>
  
Maybe you have a question: "Okay, What is the difference between a directory and a subvolume? Both can can contain something!". To further confuse you, here is what users get if they reproduce the first level hierarchy on a real machine:
+
This will produce:
  
<console>
+
{{file|name=/etc/foo.conf|desc=My foo.conf file|body=
###i## ls -l
+
# /etc/host.conf:
total 0
+
# $Header: /var/cvsroot/gentoo/src/patchsets/glibc/extra/etc/host.conf,v 1.1 2006/09/29
drwx------ 1 root root 0 May 23 12:48 SV1
+
}}
drwxr-xr-x 1 root root 0 May 23 12:48 D1
+
-rw-r--r-- 1 root root 0 May 23 12:48 F1
+
drwx------ 1 root root 0 May 23 12:48 SV2
+
</console>
+
  
Although subvolumes SV1 and SV2 have been created with special BTRFS commands they appear just as if they were ordinary directories! A subtle nuance exists, however: think again at our boxes analogy we did before and map the following concepts in the following manner:
+
=== Console ===
 
+
To display console output, use the <tt>&#60;console&#62;</tt> tag:
* a subvolume : the semi-opaque '''box'''
+
* a directory : a ''sort of'' '''item''' (that can contain something even another subvolume)
+
* a file : ''another sort of'' '''item'''
+
 
+
So, in the internal filesystem metadata SV1 and SV2 are stored in a different manner than D1 (although this is transparently handled for users). You can, however see SV1 and SV2 for what they are (subvolumes) by running the following command (subvolume numbered (0) has been mounted on /mnt):
+
  
 +
For a root console:
 +
<pre>
 
<console>
 
<console>
###i## btrfs subvolume list /mnt
+
###i## run a command as root
ID 258 top level 5 path SV1
+
ID 259 top level 5 path SV2
+
 
</console>
 
</console>
 
+
</pre>
What would we get if we create SV21 and SV22 inside of SV2? Let's try! Before going further you should be aware that a subvolume is created by invoking the magic command '''btrfs subvolume create''':
+
Produces:
 
+
 
<console>
 
<console>
###i## cd /mnt/SV2
+
###i## run a command as root
###i## btrfs subvolume create SV21
+
Create subvolume './SV21'
+
###i## btrfs subvolume create SV22
+
Create subvolume './SV22'
+
###i## btrfs subvolume list /mnt 
+
ID 258 top level 5 path SV1
+
ID 259 top level 5 path SV2
+
ID 260 top level 5 path SV2/SV21
+
ID 261 top level 5 path SV2/SV22
+
 
</console>
 
</console>
  
Again, invoking '''ls''' in /mnt/SV2 will report the subvolumes as being directories:
+
For a non-root console:
 
+
<pre>
 
<console>
 
<console>
###i## ls -l
+
$ ##i##run a command as user
total 0
+
drwx------ 1 root root 0 May 23 13:15 SV21
+
drwx------ 1 root root 0 May 23 13:15 SV22
+
 
</console>
 
</console>
 
+
</pre>
== Changing the point of view on the subvolumes hierarchy ==
+
Produces:
 
+
At some point in our boxes analogy we have talked about what we see and what we don't see depending on our location in the hierarchy. Here lies a big important point: whereas most of the BTRFS users mount the root subvolume (subvolume id = 0, we will retain the ''root subvolume'' terminology) in their VFS hierarchy thus making visible the whole hierarchy contained in the BTRFS volume, it is absolutely possible to mount only a ''subset'' of it. How that could be possible? Simple: Just specify the subvolume number when you invoke mount. For example, to mount the hierarchy in the VFS starting at subvolume SV22 (261) do the following:
+
 
+
 
<console>
 
<console>
###i## mount -o subvolid=261 /dev/loop0 /mnt
+
$ ##i##run a command as user
 
</console>
 
</console>
  
Here lies an important notion not disclosed in the previous paragraph: although both directories and subvolumes can act as containers, '''only subvolumes can be mounted in a VFS hierarchy'''. It is a fundamental aspect to remember: you cannot mount a sub-part of a subvolume in the VFS; you can only mount the subvolume in itself. Considering the hierarchy schema in the previous section, if you want to access the directory D3 you have three possibilities:
+
{{important|1=
 +
Note that we use a <tt>#</tt> prompt for <tt>root</tt> and a <tt>$</tt> prompt to denote a non-root user.}}
  
# Mount the non-named subvolume (numbered 0) and access D3 through /mnt/SV2/SV22/D3 if the non-named subvolume is mounted in /mnt
+
{{important|The <tt>##i##</tt> text tags the rest of the line as being ''user input'' ("i" is for "input"). It is then highlighted in a noticeable color so it stands out from text that is not typed in by the user.}}
# Mount the subvolume SV2 (numbered 259) and access D3 through /mnt/SV22/D3 if the the subvolume SV2 is mounted in /mnt
+
# Mount the subvolume SV22 (numbered 261) and access D3 through /mnt/D3 if the the subvolume SV22 is mounted in /mnt
+
  
This is accomplished by the following commands, respectively:
+
If you need to end highlighting of user input prior to the end of a line, use <code>##!i##</code> to mark the end of the highlighted area.
  
<console>
+
The following special character sequences are also available:
###i## mount -o subvolid=0 /dev/loop0 /mnt
+
* <code>##g##</code> - Green
###i## mount -o subvolid=259 /dev/loop0 /mnt
+
* <code>##y##</code> - Yellow
###i## mount -o subvolid=261 /dev/loop0 /mnt
+
* <code>##bl##</code> - Blue
</console>
+
* <code>##r##</code> - Red
 +
* <code>##b##</code> - Bold
  
{{fancynote|When a subvolume is mounted in the VFS, everything located "above" the subvolume is hidden. Concretely, if you mount the subvolume numbered 261 in /mnt, you only see what is under SV22, you won't see what is located above SV22 like SV21, SV2, D1, SV1, etc. }}
+
Please use the above coloring options sparingly. It is sometimes nice to use them to get wiki console output to match the colors that are displayed on a Linux console. Also note that for every color above, there is a matching <code>##!(colorcode)##</code> option to turn color off prior to end of line.
  
== The default subvolume ==
+
Here is an example of its use:<console>
 
+
# ##i##bluetoothctl
$100 questions:
+
[##g##NEW##!g##] Controller 00:02:72:C9:62:65 antec [default]
1. "If I don't put 'subvolid' in the command line, 1. how does the kernel know which one of the subvolumes it has to mount?
+
##bl##[bluetooth]##!bl###power on
2. Does Omitting the 'subvolid' means automatically 'mount subvolume numbered 0'?".
+
Changing power on succeeded
Answers:
+
##bl##[bluetooth]##!bl### ##i##agent on
1. BTRFS magic! ;-)
+
Agent registered
2. No, not necessarily, you can choose something other than the non-named subvolume.
+
##bl##[bluetooth]##!bl### ##i##scan on
 
+
Discovery started
When you create a brand new BTRFS filesystem, the system not only creates the initial the root subvolume (numbered 0) but also tags it as being the '''default subvolume'''. When you ask the operating system to mount a subvolume contained in a BTRFS volume without specifying a subvolume number, it determines which of the existing subvolumes has been tagged as "default subvolume" and mounts it. If none of the exiting subvolumes has the tag "default subvolume" (e.g. because the default subvolume has been deleted), the mount command gives up with a rather cryptic message:
+
##bl##[bluetooth]##!bl### ##i##devices
 
+
Device 00:1F:20:3D:1E:75 Logitech K760
<console>
+
##bl##[bluetooth]##!bl### ##i##pair 00:1F:20:3D:1E:75
###i## mount /dev/loop0 /mnt
+
Attempting to pair with 00:1F:20:3D:1E:75
mount: No such file or directory
+
[##y##CHG##!y##] Device 00:1F:20:3D:1E:75 Connected: yes
 +
##r##[agent]##!r## Passkey: 454358
 +
##r##[agent]##!r## Passkey: ##i##4##!i##54358
 +
##r##[agent]##!r## Passkey: ##i##45##!i##4358
 +
##r##[agent]##!r## Passkey: ##i##454##!i##358
 +
##r##[agent]##!r## Passkey: ##i##4543##!i##58
 +
##r##[agent]##!r## Passkey: ##i##45435##!i##8
 +
##r##[agent]##!r## Passkey: ##i##454358##!i##
 +
[##y##CHG##!y##] Device 00:1F:20:3D:1E:75 Paired: yes
 +
Pairing successful
 +
[##y##CHG##!y##] Device 00:1F:20:3D:1E:75 Connected: no
 +
##bl##[bluetooth]##!bl### ##i##connect 00:1F:20:3D:1E:75
 +
Attempting to connect to 00:1F:20:3D:1E:75
 +
[##y##CHG##!y##] Device 00:1F:20:3D:1E:75 Connected: yes
 +
Connection successful
 +
##bl##[bluetooth]##!bl### ##i##quit
 +
[##r##DEL##!r##] Controller 00:02:72:C9:62:65 antec [default]
 +
#
 
</console>
 
</console>
  
It is also possible to change at any time which subvolume contained in a BTRFS volume is considered the default volume. This is accomplished with '''btrfs subvolume set-default'''. The following tags the subvolume 261 as being the default:
+
=== Informational Messages ===
 +
Notes, warnings, tips, and important templates can be used for informational messages that need to be offset from the regular text flow:
  
<console>
+
<pre>{{note|this is a note}}</pre>
###i## btrfs subvolume set-default 261 /mnt
+
{{note|this is a note}}
</console>
+
  
After that operation, doing the following is exactly the same:
+
<pre>{{important|this is important}}</pre>
 +
{{important|this is important}}
  
<console>
+
<pre>{{warning|this is a warning}}</pre>
###i## mount /dev/loop0 /mnt
+
{{warning|this is a warning}}
###i## mount -o subvolid=261 /dev/loop0 /mnt
+
</console>
+
  
{{fancynote|The chosen new default subvolume must be visible in the VFS when you invoke ''btrfs subvolume set-default''' }}
+
<pre>{{tip|this is a tip}}</pre>
 +
{{tip|this is a tip}}
  
== Deleting subvolumes ==
+
Note that these templates used to be called <code>fancynote</code>, <code>fancytip</code>, etc. The "fancy" names have been deprecated but will still be supported for the forseeable future.
 
+
Question: "As subvolumes appear like directories, can I delete a subvolume by doing an rm -rf on it?".
+
Answer: Yes, you ''can'', but that way is not the most elegant, especially when it contains several gigabytes of data scattered on thousands of files, directories and maybe other subvolumes located in the one you want to remove. It isn't elegant because ''rm -rf'' could take several minutes (or even hours!) to complete whereas something else can do the same job in the fraction of a second.
+
 
+
"Huh?" Yes perfectly possible, and here is the cool goodie for the readers who arrived at this point: when you want to remove a subvolume, use '''btrfs subvolume delete''' instead of '''rm -rf'''. That btrfs command will remove the snapshots in a fraction of a second, even it contains several gigabytes of data!
+
 
+
{{fancywarning|* You can '''never''' remove the root subvolume of a BTRFS volume as '''btrfs delete''' expects a subvolume name (again: this is not a flaw in the design of BTRFS; removing the subvolume numbered 0 would destroy the entirety of a BTRFS volume...too dangerous).
+
* If the subvolume you delete was tagged as the default subvolume you will have to designate another default subvolume or explicitly tell the system which one of the subvolumes has to be mounted) }}
+
 
+
An example: considering our initial example given [[BTRFS_Fun#..._applied_to_BTRFS.21_.28or_what_is_a_volume.2Fsubvolume.29|above]] and supposing you have mounted non-named subvolume numbered 0 in /mnt, you can remove SV22 by doing:
+
 
+
<console>
+
###i## btrfs subvolume delete /mnt/SV2/SV22
+
</console>
+
 
+
Obviously the BTRFS volume will look like this after the operation:
+
  
 +
=== Kernelop ===
 +
To display kernel configuration options, we encourage you to use the <tt>kernelop</tt> template. To use the <tt>kernelop</tt> template, create an entry similar to the following example:
 
<pre>
 
<pre>
.....BTRFS Volume................................................................................................................................
+
{{kernelop|title=foo,bar|desc=
.
+
kernel options pasted from "make menuconfig"
.  (0) --+-> Subvolume SV1 (258) ---> Directory D1 --+-> File F1
+
}}
.        |                                           |
+
.        |                                          +-> File F2
+
.        |
+
.        +-> Directory D1 --+-> File F1
+
.        |                  |
+
.        |                  +-> File F2
+
.        |                  |
+
.        |                  +-> File F3
+
.        |                  |
+
.        |                  +-> Directory D11 ---> File F4
+
.        +-> File F1
+
.        |
+
.        +-> Subvolume SV2 (259) --+-> Subvolume SV21 (260)
+
.....................................................................................................................................
+
 
</pre>
 
</pre>
  
== Snapshot and subvolumes ==
+
{{note|Kernelop is colored blue to slightly resemble the blueish background from <tt>make menuconfig</tt>.}}
  
If you have a good comprehension of what a subvolume is, understanding what a snapshot is won't be a problem: a snapshot is a subvolume with some initial contents. "Some initial contents" here means an exact copy.
+
Adding this entry will give you the following output:  
 
+
{{kernelop|title=foo,bar|desc=
When you think about snapshots, think about copy-on-write: the data blocks are not duplicated between a mounted subvolume and its snapshot unless you start to make changes to the files (a snapshot can occupy nearly zero extra space on the disk). At time goes on, more and more data blocks will be changed, thus making snapshots "occupy" more and more space on the disk. It is therefore recommended to keep only a minimal set of them and remove unnecessary ones to avoid wasting space on the volume.
+
kernel options
 
+
}}
 
+
The following illustrates how to take a snaphot of the VFS root:
+
<console>
+
###i## btrfs subvolume snapshot / /snap-2011-05-23
+
Create a snapshot of '/' in '//snap-2011-05-23'
+
</console>
+
 
+
Once created, the snapshot will persist in /snap-2011-05-23 as long as you don't delete it. Note that the snapshot contents will remain exactly the same it was at the time is was taken (as long as you don't make changes... BTRFS snapshots are writable!). A drawback of having snapshots: if you delete some files in the original filesystem, the snapshot still contains them and the disk blocks can't be claimed as free space. Remember to remove unwanted snapshots and keep a bare minimal set of them.
+
 
+
== Listing and deleting snaphots ==
+
 
+
As there is no distinction between a snapshot and a subvolume, snapshots are managed with the exact same commands, especially when the time has come to delete some of them. An interesting feature in BTRFS is that snapshots are writable. You can take a snapshot and make changes in the files/directories it contains.  A word of caution: there are no undo capbilities! What has been changed has been changed forever... If you need to do several tests just take several snapshots or, better yet, snapshot your snapshot then do whatever you need in this copy-of-the-copy :-).
+
 
+
== Using snapshots for system recovery (aka Back to the Future) ==
+
 
+
Here is where BTRFS can literally be a lifeboat. Suppose you want to apply some updates via '''emerge -uaDN @world''' but you want to be sure that you can jump back into the past in case something goes seriously wrong after the system update (does libpng14 remind you of anything?!). Here is the "putting-things-together part" of the article!
+
 
+
The following only applies if your VFS root and system directories containing '''/sbin, /bin, /usr, /etc....''' are located on a BTRFS volume. To make things simple, the whole structure is supposed to be located in the SAME subvolume of the same BTRFS volume.
+
 
+
To jump back into the past you have at least two options:
+
 
+
# Fiddle with the default subvolume numbers
+
# Use the kernel command line parameters in the bootloader configuration files
+
 
+
In all cases you must take a snapshot of your VFS root *before* updating the system:
+
 
+
<console>
+
###i## btrfs subvolume snapshot / /before-updating-2011-05-24
+
Create a snapshot of '/' in '//before-updating-2011-05-24'
+
</console>
+
 
+
{{fancynote|Hint: You can create an empty file at the root of your snapshot with the name of your choice to help you easily identify which subvolume is the currently mounted one (e.g. if the snapshot has been named '''before-updating-2011-05-24''', you can use a slightly different name like '''current-is-before-updating-2011-05-24''' <nowiki>=></nowiki> '''touch /before-updating-2011-05-24/current-is-before-updating-2011-05-24'''). This is extremly useful if you are dealing with several snapshots.}}
+
 
+
There is no "better" way; it's just a question of personal preference.
+
 
+
=== Way #1: Fiddle with the default subvolume number ===
+
 
+
'''Hypothesis:
+
* Your "production" VFS root partition resides in the root subvolume (subvolid=0),'''
+
* Your /boot partition (where the bootloader configuration files are stored) is on another standalone partition
+
 
+
First search for the newly created subvolume number:
+
 
+
<console>
+
###i## btrfs subvolume list /
+
'''ID 256''' top level 5 path before-updating-2011-05-24
+
</console>
+
 
+
'256' is the ID to be retained (of course, this ID will differ in your case).
+
 
+
Now, change the default subvolume of the BTRFS volume to designate the subvolume (snapshot) ''before-updating'' and not the root subvolume then reboot:
+
 
+
<console>
+
###i## btrfs subvolume set-default 256 /
+
</console>
+
 
+
Once the system has rebooted, and if you followed the advice in the previous paragraph that suggests to create an empty file of the same name as the snapshot, you should be able to see if the mounted VFS root is the copy hold by the snapshot ''before-updating-2011-05-24'':
+
 
+
<console>
+
###i## ls -l /
+
...
+
-rw-rw-rw-  1 root root    0 May 24 20:33 current-is-before-updating-2011-05-24
+
...
+
</console>
+
 
+
The correct subvolume has been used for mounting the VFS!  Excellent! This is now the time to mount your "production" VFS root (remember the root subvolume can only be accessed via its identification number i.e ''0''):
+
 
+
<console>
+
###i## mount -o subvolid=0 /mnt
+
###i## mount
+
...
+
/dev/sda2 on /mnt type btrfs (rw,subvolid=0)
+
</console>
+
 
+
Oh by the way, as the root subvolume is now mounted in <tt>/mnt</tt> let's try something, just for the sake of the demonstration:
+
 
+
<console>
+
###i## ls /mnt
+
...
+
drwxr-xr-x  1 root root    0 May 24 20:33 current-is-before-updating-2011-05-24
+
...
+
###i## btrfs subvolume list /mnt
+
ID 256 top level 5 path before-updating-2011-05-24
+
</console>
+
 
+
No doubt possible :-)
+
Time to rollback! For this '''rsync''' will be used in the following way:
+
<console>
+
###i## rsync --progress -aHAX --exclude=/proc --exclude=/dev --exclude=/sys --exclude=/mnt / /mnt
+
</console>
+
 
+
Basically we are asking rsync to:
+
* preserve timestamps, hard and symbolic links, owner/group IDs, ACLs and any extended attributes (refer to the rsync manual page for further details on options used) and to report its progression
+
* ignore the mount points where virtual filesystems are mounted (procfs, sysfs...)
+
* avoid a re-recursion by reprocessing /mnt (you can speed up the process by adding some extra directories if you are sure they don't hold any important changes or any change at all like /var/tmp/portage for example).
+
 
+
Be patient! The resync may take several minutes or hours depending on the amount of data amount to process...
+
 
+
Once finished, you will have to set the default subvolume to be the root subvolume:
+
 
+
<console>
+
###i## btrfs subvolume set-default 0 /mnt
+
ID 256 top level 5 path before-updating-2011-05-24
+
</console>
+
 
+
{{fancywarning|'''DO NOT ENTER / instead of /mnt in the above command; it won't work and you will be under the snapshot before-updating-2011-05-24 the next time the machine reboots.'''
+
  
The reason is that subvolume number must be "visible" from the path given at the end of the '''btrfs subvolume set-default''' command line. Again refer the boxes analogy: in our context we are in a subbox numbered 256 which is located *inside* the box numbered 0 (so it can't see neither interfere with it). [TODO: better explain]
+
Here's a more concrete example:
 +
{{kernelop|title=File systems|desc=
 +
<M> Second extended fs support         
 +
[ ]   Ext2 extended attributes         
 +
[ ]  Ext2 execute in place support   
 +
<M> Ext3 journalling file system support
 
}}
 
}}
  
Now just reboot and you should be in business again! Once you have rebooted just check if you are really under the right subvolume:
+
Examples of usage:  
 +
* [[Package:AMD Catalyst Video Drivers]]
 +
* [[Package:ACPI Daemon]]
 +
* [[Microcode]]
  
<console>
+
=== Discussion Pages ===
###i## ls /
+
...
+
drwxr-xr-x  1 root root    0 May 24 20:33 current-is-before-updating-2011-05-24
+
...
+
###i## btrfs subvolume list /
+
ID 256 top level 5 path before-updating-2011-05-24
+
</console>
+
  
At the right place? Excellent! You can now  delete the snapshot if you wish, or better: keep it as a lifeboat of "last good known system state."
+
In MediaWiki, every "regular" wiki page has a corresponding "Talk" or "Discussion" page which has a page name prefixed by "Talk:" -- you can get to this page by going to the "Action" menu, and then choosing the "Discussion" menu item. These talk pages are typically used to discuss the edits that are going on in the "main" wiki page. The problem with talk pages is that they are kind of a pain to use. However, we have a way to fix that. If you want to enable a DISQUS-based mini-forum on a talk page, insert the following wikitext on the Talk page:
  
=== Way #2: Change the kernel command line in the bootloader configuration files ===
+
<pre>
 +
{{DISQUS}}
 +
</pre>
  
First search for the newly created subvolume number:
+
...and presto! You will now have DISQUS-powered mini-forums to discuss whatever you want about your wiki page.
  
<console>
+
== Marking Pages as Needing Updates ==
###i## btrfs subvolume list /
+
'''ID 256''' top level 5 path before-updating-2011-05-24
+
</console>
+
  
'256' is the ID to be retained (can differ in your case).
+
If you find outdated wiki content, but you don't have the time or ability to update it, add one of the following templates to the wikitext of the page. This will add the page to the [[:Category:Needs Updates|Needs Updates Category]] so we can identify pages that need updating:
 
+
Now with your favourite text editor, edit the adequate kernel command line in your bootloader configuration (<tt>/etc/boot.conf</tt>). This file contains is typically organized in several sections (one per kernel present on the system plus some global settings), like the excerpt below:
+
  
 
<pre>
 
<pre>
set timeout=5
+
{{PageNeedsUpdates}}
set default=0
+
{{SectionNeedsUpdates}}
 
+
# Production kernel
+
menuentry "Funtoo Linux production kernel (2.6.39-gentoo x86/64)" {
+
  insmod part_msdos
+
  insmod ext2
+
  ...
+
  set root=(hd0,1)
+
  linux /kernel-x86_64-2.6.39-gentoo root=/dev/sda2
+
  initrd /initramfs-x86_64-2.6.39-gentoo
+
}
+
...
+
 
</pre>
 
</pre>
  
Find the correct kernel line and add one of the following statements after root=/dev/sdX:
 
  
<pre>
+
Examples of usage:
rootflags=subvol=before-updating-2011-05-24
+
* [[UEFI Install Guide]]
  - Or -
+
* [[Package:MediaWiki]]
rootflags=subvolid=256
+
* [[Clang]]
</pre>
+
  
{{fancywarning|If the kernel your want to use has been generated with Genkernel, you '''MUST''' use ''real_rootflags<nowiki>=</nowiki>subvol<nowiki>=</nowiki>''... instead of ''rootflags<nowiki>=</nowiki>subvol''<nowiki>=</nowiki>... at the penalty of not having your rootflags taken into consideration by the kernel on reboot. }}
+
=== Inline Code ===
  
 
+
To emphasize commands, and other technical jargon when they appear inline in a paragraph, use the <nowiki>{{c}}</nowiki> template. When referencing files, use the <nowiki>{{f}}</nowiki> template.
Applied to the previous example you will get the following if you referred the subvolume by its name:
+
  
 
<pre>
 
<pre>
set timeout=5
+
The {{f|/etc/fstab}} file is an important one. Another important file is {{f|/boot/grub/grub.cfg}}. The {{c|emerge}} command is really nifty.
set default=0
+
 
+
# Production kernel
+
menuentry "Funtoo Linux production kernel (2.6.39-gentoo x86/64)" {
+
  insmod part_msdos
+
  insmod ext2
+
  ...
+
  set root=(hd0,1)
+
  linux /kernel-x86_64-2.6.39-gentoo root=/dev/sda2 rootflags=subvol=before-updating-2011-05-24
+
  initrd /initramfs-x86_64-2.6.39-gentoo
+
}
+
...
+
 
</pre>
 
</pre>
  
Or you will get the following if you referred the subvolume by its identification number:
+
This example produces the following output:
  
<pre>
+
The {{f|/etc/fstab}} file is an important one. Another important file is {{f|/boot/grub/grub.cfg}}. The {{c|emerge}} command is really nifty.
set timeout=5
+
set default=0
+
  
# Production kernel
+
{{important|1=
menuentry "Funtoo Linux production kernel (2.6.39-gentoo x86/64)" {
+
The &#60;tt&#62; tag has been deprecated for the purpose of tagging inline code, to conform with HTML5, and the previous use of the &#60;code&#62; tag is discouraged. It is more maintainable to use the <nowiki>{{c}}</nowiki> template. }}
  insmod part_msdos
+
  insmod ext2
+
  ...
+
  set root=(hd0,1)
+
  linux /kernel-x86_64-2.6.39-gentoo root=/dev/sda2 rootflags=subvolid=256
+
  initrd /initramfs-x86_64-2.6.39-gentoo
+
}
+
...
+
</pre>
+
  
Once the modifications are done, save your changes and take the necessary extra steps to commit the configuration changes on the first sectors of the disk if needed (this mostly applies to the users of LILO; Grub and SILO do not need to be refreshed) and reboot.
+
=== Slideshow ===
  
Once the system has rebooted and if you followed the advice in the previous paragraph that suggests to create an empty file of the same name as the snapshot, you should be able to see if the mounted VFS root is the copy hold by the snapshot ''before-updating-2011-05-24'':
+
Any page has the capability of displaying a slideshow. Adding a slideshow to a page involves three steps:
  
<console>
+
# Upload Images
###i## ls -l /
+
# Define Slides
...
+
# Add Slideshow to page
-rw-rw-rw-  1 root root    0 May 24 20:33 current-is-before-updating-2011-05-24
+
...
+
</console>
+
  
The correct subvolume has been used for mounting the VFS!  Excellent! This is now the time to mount your "production" VFS root (remember the root subvolume can only be accessed via its identification number 0):
+
==== Upload Images ====
  
<console>
+
To upload images, head to [[Special:Upload]] and upload a file. It is highly recommended to upload JPEG format images in high resolution -- MediaWiki will handle scaling JPEG automatically, saving bandwidth, but does not do this for PNG. Make sure that all images you upload have the same dimensions. When you upload, make note of the '''Destination Filename''' field -- this is the name that the upload will use when you reference it in your slide. It is recommended that you choose a simple descriptive name ending in ".jpg" for the '''Destination Filename'''.
###i## mount -o subvolid=0 /mnt
+
###i## mount
+
...
+
/dev/sda2 on /mnt type btrfs (rw,subvolid=0)
+
</console>
+
  
Time to rollback! For this '''rsync''' will be used in the following way:
+
==== Define Slides ====
<console>
+
###i## rsync --progress -aHAX --exclude=/proc --exclude=/dev --exclude=/sys --exclude=/mnt / /mnt
+
</console>
+
  
Here, please refer to what has been said in [[BTRFS_Fun#Way_.231:_Fiddle_with_the_default_subvolume_number|Way #1]] concerning the used options in rsync. Once everything is in place again, edit your bootloader configuration to remove the rootflags/real_rootflags kernel parameter, reboot and check if you are really under the right subvolume:
+
Once images have been uploaded, you must define slides. To define slides on a page, you enter special semantic information about the slide on the page that it will be displayed, in the following format:
  
<console>
+
<pre><nowiki>
###i## ls /
+
{{#subobject:|slideIndex=0|slideCaption=
...
+
== Wikitext Here ==
drwxr-xr-x  1 root root    0 May 24 20:33 current-is-before-updating-2011-05-24
+
This is a fantastic slide!
...
+
|slideImage=File:Fruit.jpg|slideLink=PageName}}
###i## btrfs subvolume list /
+
</nowiki></pre>
ID 256 top level 5 path current-is-before-updating-2011-05-24
+
</console>
+
  
At the right place? Excellent! You can now  delete the snapshot if you wish, or better: keep it as a lifeboat of "last good known system state."
+
Here are some important instructions regarding defining slides:
  
= Some BTRFS practices / returns of experience / gotchas =
+
* <code>slideIndex</code> must be 0 for the first slide, 1 for the second slide, etc. Numbers must be unique and incrementing from zero, and not doing this will result in slideshow display errors (but can be easily fixed by correcting the wikitext.)
 +
* <code>slideCaption=</code> can contain wikitext, such as headings and links. The best way to enter <code>slideCaption</code> is as above -- type a literal <code>slideCaption=</code>, followed by enter, then specify your wikitext, and terminate the caption by a single pipe character on the following line. Pipe characters are used to separate arguments from each other.
 +
* Specify your image name in the <code>slideImage</code> field. Your slideImage will have a name of <code>File:myname.jpg</code>, where <code>myname.jpg</code> is the '''Destination Filename''' you used when uploading the image.
 +
* An optional parameter called <code>slideLink=</code> can be provided to allow the image to be clickable and link to another wiki page. If it is omitted, then the image will not be clickable.
  
* Although BTRFS is still evolving, at the date of writing it (still) is '''an experimental filesystem and should be not be used for production systems and for storing critical data''' (even if the data is non critical, having backups on a partition formatted with a "stable" filesystem like Reiser or ext3/4 is recommended).
+
==== Add Slideshow to Page ====
* From time to time some changes are brought to the metadata (BTRFS format is not definitive at date of writing) and a BTRFS partition could not be used with older Linux kernels (this happened with Linux 2.6.31).
+
* More and more Linux distributions are proposing the filesystem as an alternative for ext4
+
* Some reported gotchas: [https://btrfs.wiki.kernel.org/index.php/Gotchas https://btrfs.wiki.kernel.org/index.php/Gotchas]
+
* Playing around with BTFRS can be a bit tricky especially when dealing with default volumes and mount point (again: the box analogy)
+
* Using compression (e.g. LZO =>> mount -o compress=lzo) on the filesystem can improve the throughput performance, however many files nowadays are already compressed at application level (music, pictures, videos....).
+
* Using space caching capabilities (mount -o space_cache) seems to brings some extra slight performance improvements.
+
* There is very [https://lkml.org/lkml/2010/6/18/144 interesting discussion on BTRFS design limitations with B-Trees] lying on LKML. We ''strongly'' encourage you to read about on
+
  
== Deploying a Funtoo instance in a subvolume other than the root subvolume ==
+
Once the slides have been added to the page, you can add the following text to your page at the point you'd like the slideshow to appear:
 +
<pre>
 +
{{Slideshow}}
 +
</pre>
  
Some Funtoo core devs have used BTRFS for many months and no major glitches have been reported so far (except an non-aligned memory access trap on SPARC64 in a checksum calculation routine; minor latest kernels may brought a correction) except a long time ago but this was more related to a kernel crash due to a bug that corrupted some internal data rather than the filesystem code in itself.
+
=== YouTube Videos (Screencasts, etc.) ===
 
+
The following can simplify your life in case of recovery '''(not tested)''':
+
 
+
When you prepare the disk space that will hold the root of your future Funtoo instance (and so, will hold /usr /bin /sbin /etc etc...), don't use the root subvolume but take an extra step to define a subvolume like illustrated below:
+
 
+
<console>
+
###i## fdisk /dev/sda2
+
....
+
###i## mkfs.btrfs /dev/sda2
+
###i## mount /dev/sda2 /mnt/funtoo
+
###i## subvolume create /mnt/funtoo /mnt/funtoo/live-vfs-root-20110523
+
###i## chroot /mnt/funtoo/live-vfs-root-20110523 /bin/bash
+
</console>
+
 
+
Then either:
+
 
+
* Set the default subvolume /live-vfs-root-20110523 as being the default subvolume (btrfs subvolume set-default.... remember to inspect the subvolume identification number)
+
* Use rootflag / real_rootfsflags (always use real_rootfsflags for kernel generated with Genkernel) on the kernel command line in your bootloader configuration file
+
 
+
Technically speaking, it won't change your life BUT at system recovery: when you want to rollback to a functional VFS root copy because something happened (buggy system package, too aggressive cleanup that removed Python, dead compiling toolchain...) you can avoid a time costly rsync but at the cost of putting a bit of overhead over your shoulders when taking a snapshot.
+
 
+
Here again you have two ways to recover the system:
+
 
+
* '''fiddling with the default subvolume:'''
+
** Mount to the no named volume somewhere (e.g. '''mount -o subvolid=0 /dev/sdX /mnt''')
+
** Take a snapshot (remember to check its identification number) of your current subvolume and store it under the root volume you just have just mounted ('''btrfs snapshot create / /mnt/before-updating-20110524''') -- (Where is the "frontier"? If 0 is monted does its contennts also appear in the taken snashot located on the same volume?)
+
** Update your system or do whatever else "dangerous" operation
+
** If you need to return to the latest good known system state, just set the default subvolume to use to the just taken snapshot ('''btrfs subvolume set-default ''<snapshotnumber here>'' /mnt''')
+
** Reboot
+
** Once you have  rebooted, just mount the root subvolume again and delete the subvolume that correspond to the failed system update ('''btrfs subvolume delete /mnt/<buggy VFS rootsnapshot name here>''')
+
 
+
* '''fiddling with the kernel command line:'''
+
** Mount to the no named volume somewhere (e.g. '''mount -o subvolid=0 /dev/sdX /mnt''')
+
** Take a snapshot (remember to check its identification number) of your current subvolume and store it under the root volume you just have just mounted ('''btrfs snapshot create / /mnt/before-updating-20110524''') -- (Where is the "frontier"? If 0 is mounted does its contents also appear in the taken snapshot located on the same volume?)
+
** Update your system or do whatever else "dangerous" operation
+
** If you need to return to the latest good known system state, just set the rootflags/real_rootflags as demonstrated in previous paragraphs in your loader configuration file
+
** Reboot
+
** Once you have  rebooted, just mount the root subvolume again and delete the subvolume that correspond to the failed system update ('''btrfs subvolume delete /mnt/<buggy VFS rootsnapshot name here>''')
+
 
+
== Space recovery / defragmenting the filesystem ==
+
 
+
{{Fancytip|From time to time it is advised to ask for re-optimizing the filesystem structures and data blocks in a subvolume. In BTRFS terminology this is called a defragmentation and it only be performed when the subvolume is mounted in the VFS (online defragmentation):}}
+
 
+
<console>
+
###i## btrfs filesystem defrag /mnt
+
</console>
+
 
+
You can still access the subvolume, even change its contents, while a defragmentation is running.
+
 
+
It is also a good idea to remove the snapshots you don't use anymore especially if huge files and/or lots of files are changed because snapshots will still hold some blocks that could be reused.
+
 
+
== SSE 4.2 boost ==
+
 
+
If your CPU supports hardware calculation of CRC32 (e.g. since Intel Nehalem series and later and AMD Bulldozer series), you are encouraged to enable that support in your kernel since BTRFS makes an aggressive use of those. Just check you have enabled ''CRC32c INTEL hardware acceleration'' in  ''Cryptographic API'' either as a module or as a built-in feature
+
 
+
= Recovering an apparent dead BTRFS filesystem =
+
 
+
Dealing with a filesystem metadata coherence is a critical in  a filesystem design. Losing some data blocks (i.e. having some corrupted files) is less critical than having a screwed-up and unmountable filesystem especially if you do backups on a regular basis '''(the rule with BTRFS is *do backups*, BTRFS has no mature filesystem repair tool and you *will* end up in having to re-create your filesystem from scratch again sooner or later).'''
+
 
+
== Mounting with recovery option (Linux 3.2 and beyond) ==
+
 
+
If you are using '''Linux 3.2 and later (only!)''', you can use the ''recovery'' option to make BTRFS seek for a usable copy of tree root (several copies of it exists on the disk). Just mount your filesystem as:
+
 
+
<console>
+
###i## mount -o recovery /dev/yourBTFSvolume /mount/point
+
</console>
+
 
+
== btrfs-select-super / btrfs-zero-log ==
+
 
+
Two other handy tools exist but they are not deployed by default by ''sys-fs/btrfs-progs'' (even ''btrfs-progs-9999'') ebuilds because they only lie in the branch ''"next"'' of the'' btrfs-progs'' Git repository:
+
 
+
* btrfs-select-super
+
* btrfs-zero-log
+
 
+
=== Building the btrfs-progs goodies ===
+
+
The two tools this section is about are not build by default and Funtoo ebuilds does not build them as well for the moment. So you must build them manually:
+
 
+
<console>
+
###i## mkdir ~/src
+
###i## cd ~/src
+
###i## git clone git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
+
###i## cd btrfs-progs
+
###i## make && make btrfs-select-super && make btrfs-zero-log
+
</console>
+
 
+
{{fancynote|In the past, ''btrfs-select-super'' and ''btrfs-zero-log'' were lying in the git-next branch, this is no longer the case and those tools are available in the master branch }}
+
 
+
=== Fixing dead superblock ===
+
 
+
In case of a corrupted superblock, start by asking btrfsck to use an alternate copy of the superblock instead of the superblock #0. This is achieved via the -s option followed by the number of the alternate copy you wish to use. In the following example we ask for using the superblock copy #2 of /dev/sda7:
+
 
+
<console>
+
###i## ./btrfsck --s 2 /dev/sd7
+
</console>
+
 
+
When btrfsck is happy, use btrfs-super-select to restore the default superblock (copy #0) with a clean copy.  In the following example we ask for restoring the superblock of /dev/sda7 with its copy #2:
+
 
+
<console>
+
###i## ./btrfs-super-select -s 2  /dev/sda7
+
</console>
+
 
+
Note that this will overwrite all the other supers on the disk, which means you really only get one shot at it. 
+
 
+
'''If you run btrfs-super-select prior prior to figuring out which one is good, you've lost your chance to find a good one.'''
+
 
+
=== Clearing the BTRFS journal ===
+
 
+
''' This will only help with one specific problem! '''
+
 
+
If you are unable to mount a BTRFS partition after a hard shutdown, crash or power loss, it may be due to faulty log playback in kernels prior to 3.2.  The first thing to try is updating your kernel, and mounting.  If this isn't possible, an alternate solution lies in truncating the BTRFS journal, but only if you see "replay_one_*" functions in the oops callstack.
+
 
+
To truncate the journal of a BTRFS partition (and thereby lose any changes that only exist in the log!), just give the filesystem to process to ''btrfs-zero-log'':
+
 
+
<console>
+
###i## ./btrfs-zero-log /dev/sda7
+
</console>
+
 
+
This is not a generic technique, and works by permanently throwing away a small amount of potentially good data.
+
 
+
== Using btrfsck ==
+
 
+
{{fancywarning|Extremely experimental...}}
+
 
+
If one thing is famous in the BTRFS world it would be the so-wished fully functional ''btrfsck''. A read-only version of the tool was existing out there for years, however at the begining of 2012, BTRFS developers made a public and very experimental release: the secret jewel lies in the branch ''dangerdonteveruse'' of the BTRFS Git repository hold by Chris Mason on kernel.org.
+
 
+
<console>
+
###i## git clone git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
+
###i## cd btrfs-progs
+
###i## git checkout dangerdonteveruse
+
###i## make
+
</console>
+
 
+
So far the tool can:
+
* Fix errors in the extents tree and in blocks groups accounting
+
* Wipe the CRC tree and create a brand new one (you can to mount the filesystem with CRC checking disabled )
+
 
+
To repair:
+
 
+
<console>
+
###i## btrfsck --repair /dev/''yourBTRFSvolume''
+
</console>
+
 
+
To wipe the CRC tree:
+
<console>
+
###i## btrfsck --init-csum-tree /dev/''yourBTRFSvolume''
+
</console>
+
  
Two other options exist in the source code: ''--super'' (equivalent of btrfs-select-super ?) and ''--init-extent-tree'' (clears out any extent?)
+
Screencasting is an easy method to explain complex tasks. Take for instance <code>youtu.be/5KDei5mBfSg</code> and chop off the id and insert it into the following syntax to produce a video example.
  
= Final words =
+
<pre>{{#widget:YouTube16x9|id=5KDei5mBfSg}}</pre>
 +
{{#widget:YouTube16x9|id=5KDei5mBfSg}}
  
We give the great lines here but BTRFS can be very tricky especially when several subvolumes coming from several BTRFS volumes are used. And remember: BTRFS is still experimental at date of writing :)
+
{{tip|The sample video above explains how to create your own screencasts under Funtoo Linux.}}
  
== Lessons learned ==
+
Most YouTube videos are in 16x9 format and should use the <code>YouTube16x9</code> widget. There is also a <code>YouTube4x3</code> widget for videos with a 4x3 aspect ratio.
* Very interesting but still lacks some important features present in ZFS like RAID-Z, virtual volumes, management by attributes, filesystem streaming, etc.
+
{{note|These YouTube widgets have been updated to be mobile-friendly.}}
* Extremly interesting for Gentoo/Funtoo systems partitions (snapshot/rollback capabilities). However not integrated in portage yet.
+
* If possible, use a file monitoring tool like TripWire this is handy to see what file has been corrupted once the filesystem is recovered or if a bug happens
+
* '''It is highly advised to not use the root subvolume when deploying a new Funtoo instance''' or put any kind of data on it in a more general case. Rolling back a data snapshot will be much easier and much less error prone (no copy process, just a matter of 'swapping' the subvolumes).  
+
* Backup, backup backup your data! ;)
+
  
[[Category:Labs]]
+
[[Category:Wiki Development]]
[[Category:Articles]]
+
[[Category:Featured]]
+
[[Category:Filesystems]]
+
{{ArticleFooter}}
+

Revision as of 07:38, January 4, 2015

Thanks for your interest in contributing to the the Funtoo wiki!

Types of Edits

Before we get started, let's review what changes are okay to make, and what changes are not okay:

Type of ChangeOkay?
Grammar/spelling fixesYes
New wiki contentYes
New package informationYes
Adding to existing articleMaybe -- see below
Adding missing/incomplete informationYes
Making correctionsYes
Adding work-arounds to problems experiencedNo - open bug first on bug tracker.
Important

Note that if you experience some problem with Funtoo Linux, during installation or otherwise, the proper course of action is to not add a work-around to our documentation, but to open a bug on our bug tracker. This is important because the problem you experienced may be a legitimate bug and the solution may be to fix the bug rather than add a work-around to our documentation. We may end up fixing a bug, making a documentation fix, or possibly both.

Basics

Here is a list of basic wiki information that you will need to know to get started:

  • First, to perform edits on the wiki, you must Create a Funtoo account and log in.
  • You can create a new page by navigating to http://www.funtoo.org/New_Page_Name. Underscores are the equivalent of spaces. Then select "Create" under the "Actions" menu.
  • Whether creating a new page or editing an existing page by clicking "Edit", you will be presented with Web-based text editor that allows you to modify the wikitext of the page. The wikitext is rendered to produce the document you see when you view the page normally.
  • Another fun thing you can do is click on your name under the "Account" menu once you have logged in. This will bring you to your "User" page. Then click "Create with Form" unde the "Actions" menu and enter your geographic and other information. This will allow you to be displayed on our Usermap and will also allow your full name to be displayed on Ebuild pages for which you are an author. It's generally a good idea to do this.
Tip

The following sections document how to use wikitext and Funtoo templates on the Funtoo wiki.

Paragraphs

To create a new paragraph, insert a blank line between two lines of text. If a blank line doesn't exist between two lines of wikitext, they will be combined into a single flowing paragraph.

If you leave leading whitespace at the beginning of a line, MediaWiki will render it as pre-formatted text. Beware of this. Here's an example:

foobar

This can rear its ugly head when specifying template parameters, so you will get this:

Note
ugh!

...instead of this:

Note

This looks much better!

Page and Section Capitalization

In general, capitalize all words in page names and section heading except:

  • Articles: a, an, the
  • Coordinating Conjunctions: and, but, or, for, nor, etc.
  • Prepositions (fewer than five letters): on, at, to, from, by, etc.

Document Hierarchy

Use section headings to create a document hierarchy for your page. These will define the table of contents that appears at the top of the wiki page. Create chapters, sections and sub-sections as follows:

= Page Title =

== Chapter Title ==

=== Section Title ===

==== SubSection Title ====

Note

By default, Table of Contents is disabled on the Funtoo wiki. If you would like to enable the TOC, you can place a __TOC__ on a blank line where you'd like the Table of Contents to appear, or place __FORCETOC__ on a blank line anywhere in the wikitext to force the TOC to appear at the top of the page.

In general, when creating new documents, it's best to use level-3 (three "="'s) Section Titles to break up content. Level-2 Section Titles are best used for major sections of larger documents. Use them infrequently. Level-1 Section Titles generally do not need to be used.

Links

Internal links to other wiki pages can be specified as [[pagename]]. To specify an alternate name for the link, use [[pagename|my link name]].

For external links, use [http://funtoo.org my link] to specify a URL. If you want the URL to appear in the wikitext, you can specify it without brackets: http://forums.funtoo.org.

Lists

MediaWiki supports a number of list formats:

  • Unordered List
  • Unordered Item 2
    • Unordered sub-item
  1. Ordered List
  2. Ordered Item 2
    1. Ordered sub-item
Term
This is called a "definition list". It is used when defining various terms.

If you need to quote a portion of text from another site, use <blockquote> as follows:

Wikipedia (ˌwɪkɨˈpiːdiə/ or wɪkiˈpiːdiə/ wik-i-pee-dee-ə) is a collaboratively edited, multilingual, free-access, free content Internet encyclopedia that is supported and hosted by the non-profit Wikimedia Foundation. Volunteers worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including over 4.5 million in the English Wikipedia. Anyone who can access the site can edit almost any of its articles, which on the Internet comprise[4] the largest and most popular general reference work.[5][6][7][8][9] In February 2014, The New York Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google, the largest with 1.2 billion unique visitors."[10]

Literal Text and HTML Symbols

Here is wikitext for the section above, which I am displaying by placing the literal wikitext between a <pre> and </pre> tag. If you want to disable wikitext processing for an inline span of text, use <nowiki> and </nowiki>. If you want to print out a tag literally, use &#60; and &#62; (In the wikitext, I used &amp;#60; and &amp;#62 to display these!)

* Unordered List
* Unordered Item 2
** Unordered sub-item

# Ordered List
# Ordered Item 2
## Ordered sub-item

;Term: This is called a "definition list". It is used when defining various terms.

If you need to quote a portion of text from another site, use <tt><blockquote></tt> as follows:

<blockquote>
Wikipedia (ˌwɪkɨˈpiːdiə/ or wɪkiˈpiːdiə/ wik-i-pee-dee-ə) is a collaboratively edited, multilingual, free-access, 
free content Internet encyclopedia that is supported and hosted by the non-profit Wikimedia Foundation. Volunteers
worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including over 4.5 million in the 
English Wikipedia. Anyone who can access the site can edit almost any of its articles, which on the Internet 
comprise[4] the largest and most popular general reference work.[5][6][7][8][9] In February 2014, The New York 
Times reported that Wikipedia is ranked fifth globally among all websites stating, "With 18 billion page views 
and nearly 500 million unique visitors a month..., Wikipedia trails just Yahoo, Facebook, Microsoft and Google, 
the largest with 1.2 billion unique visitors."[10]
</blockquote>

Linking to Packages

To link to a package page, use the Package template:

{{Package|sys-apps/portage}}

This template will create a link to the official wiki page for sys-apps/portage, and render using the official "English" page name, as follows:

Portage (Funtoo)

If you specify a yet-to-be-documented ebuild, it will render like this (which is okay -- it will encourage people to document it):

sys-foo/undocumented-ebuild (package not on wiki - please add)

Tables

Instead of using traditional MediaWiki table wikitext, use the following format:

{{TableStart}}
<tr class="info"><th>Header 1</th><th>Header 2</th></tr>
<tr><td>Value 1</td><td>Value 2</td></tr>
<tr><td>Value 3</td><td>Value 4</td></tr>
{{TableEnd}}

This wil render as follows:

Header 1Header 2
Value 1Value 2
Value 3Value 4
Tip

This table syntax has an added benefit of creating a responsive table that renders properly on mobile devices.

It is possible to use the following CSS classes with tr (rows) and td/th elements to color them as desired:

Class Name
success
info
warning
active
danger

Displaying Source Code

To display source code, use can use the file template, specifying a lang= parameter:

{{file|name=foobar|lang=python|desc=foobarosity|body=
import system
}}

This will produce:

foobar (python source code) - foobarosity
import system

The parameters name (filename), lang (language for syntax highlighting) and desc (Description, appearing as a caption) are optional. For a list of supported languages, see this list.


Important

If you need to display the pipe ("|") character within the body of a file template, replace each "|" with {{!}} -- otherwise your file contents will not display properly. This is necessary because {{file}} is a template and the "|" character is used as a delimiter for arguments to the template.

Displaying Text File Contents

For displaying the contents of non-programming language text files (like config files), you have two options. You can enclose your lines within <pre> tags, or use the new file template. The file template is used like so:

{{file|name=/etc/foo.conf|desc=My foo.conf file|body=
# /etc/host.conf:
# $Header: /var/cvsroot/gentoo/src/patchsets/glibc/extra/etc/host.conf,v 1.1 2006/09/29
}}

This will produce:

/etc/foo.conf - My foo.conf file
# /etc/host.conf:
# $Header: /var/cvsroot/gentoo/src/patchsets/glibc/extra/etc/host.conf,v 1.1 2006/09/29

Console

To display console output, use the <console> tag:

For a root console:

<console>
###i## run a command as root
</console>

Produces:

# run a command as root

For a non-root console:

<console>
$ ##i##run a command as user
</console>

Produces:

$ run a command as user
Important

Note that we use a # prompt for root and a $ prompt to denote a non-root user.

Important

The ##i## text tags the rest of the line as being user input ("i" is for "input"). It is then highlighted in a noticeable color so it stands out from text that is not typed in by the user.

If you need to end highlighting of user input prior to the end of a line, use ##!i## to mark the end of the highlighted area.

The following special character sequences are also available:

  • ##g## - Green
  • ##y## - Yellow
  • ##bl## - Blue
  • ##r## - Red
  • ##b## - Bold

Please use the above coloring options sparingly. It is sometimes nice to use them to get wiki console output to match the colors that are displayed on a Linux console. Also note that for every color above, there is a matching ##!(colorcode)## option to turn color off prior to end of line.

Here is an example of its use:
# bluetoothctl 
[NEW] Controller 00:02:72:C9:62:65 antec [default]
[bluetooth]#power on
Changing power on succeeded
[bluetooth]# agent on
Agent registered
[bluetooth]# scan on
Discovery started
[bluetooth]# devices
Device 00:1F:20:3D:1E:75 Logitech K760
[bluetooth]# pair 00:1F:20:3D:1E:75
Attempting to pair with 00:1F:20:3D:1E:75
[CHG] Device 00:1F:20:3D:1E:75 Connected: yes
[agent] Passkey: 454358
[agent] Passkey: 454358
[agent] Passkey: 454358
[agent] Passkey: 454358
[agent] Passkey: 454358
[agent] Passkey: 454358
[agent] Passkey: 454358
[CHG] Device 00:1F:20:3D:1E:75 Paired: yes
Pairing successful
[CHG] Device 00:1F:20:3D:1E:75 Connected: no
[bluetooth]# connect 00:1F:20:3D:1E:75
Attempting to connect to 00:1F:20:3D:1E:75
[CHG] Device 00:1F:20:3D:1E:75 Connected: yes
Connection successful
[bluetooth]# quit
[DEL] Controller 00:02:72:C9:62:65 antec [default]
#

Informational Messages

Notes, warnings, tips, and important templates can be used for informational messages that need to be offset from the regular text flow:

{{note|this is a note}}
Note

this is a note

{{important|this is important}}
Important

this is important

{{warning|this is a warning}}
Warning

this is a warning

{{tip|this is a tip}}
Tip

this is a tip

Note that these templates used to be called fancynote, fancytip, etc. The "fancy" names have been deprecated but will still be supported for the forseeable future.

Kernelop

To display kernel configuration options, we encourage you to use the kernelop template. To use the kernelop template, create an entry similar to the following example:

{{kernelop|title=foo,bar|desc=
kernel options pasted from "make menuconfig"
}} 
Note

Kernelop is colored blue to slightly resemble the blueish background from make menuconfig.

Adding this entry will give you the following output: Under foo-->bar:

kernel options

Here's a more concrete example: Under File systems:

<M> Second extended fs support          
[ ]   Ext2 extended attributes          
[ ]   Ext2 execute in place support     
<M> Ext3 journalling file system support

Examples of usage:

Discussion Pages

In MediaWiki, every "regular" wiki page has a corresponding "Talk" or "Discussion" page which has a page name prefixed by "Talk:" -- you can get to this page by going to the "Action" menu, and then choosing the "Discussion" menu item. These talk pages are typically used to discuss the edits that are going on in the "main" wiki page. The problem with talk pages is that they are kind of a pain to use. However, we have a way to fix that. If you want to enable a DISQUS-based mini-forum on a talk page, insert the following wikitext on the Talk page:

{{DISQUS}}

...and presto! You will now have DISQUS-powered mini-forums to discuss whatever you want about your wiki page.

Marking Pages as Needing Updates

If you find outdated wiki content, but you don't have the time or ability to update it, add one of the following templates to the wikitext of the page. This will add the page to the Needs Updates Category so we can identify pages that need updating:

{{PageNeedsUpdates}}
{{SectionNeedsUpdates}}


Examples of usage:

Inline Code

To emphasize commands, and other technical jargon when they appear inline in a paragraph, use the {{c}} template. When referencing files, use the {{f}} template.

The {{f|/etc/fstab}} file is an important one. Another important file is {{f|/boot/grub/grub.cfg}}. The {{c|emerge}} command is really nifty.

This example produces the following output:

The /etc/fstab file is an important one. Another important file is /boot/grub/grub.cfg. The emerge command is really nifty.

Important

The <tt> tag has been deprecated for the purpose of tagging inline code, to conform with HTML5, and the previous use of the <code> tag is discouraged. It is more maintainable to use the {{c}} template.

Slideshow

Any page has the capability of displaying a slideshow. Adding a slideshow to a page involves three steps:

  1. Upload Images
  2. Define Slides
  3. Add Slideshow to page

Upload Images

To upload images, head to Special:Upload and upload a file. It is highly recommended to upload JPEG format images in high resolution -- MediaWiki will handle scaling JPEG automatically, saving bandwidth, but does not do this for PNG. Make sure that all images you upload have the same dimensions. When you upload, make note of the Destination Filename field -- this is the name that the upload will use when you reference it in your slide. It is recommended that you choose a simple descriptive name ending in ".jpg" for the Destination Filename.

Define Slides

Once images have been uploaded, you must define slides. To define slides on a page, you enter special semantic information about the slide on the page that it will be displayed, in the following format:

{{#subobject:|slideIndex=0|slideCaption=
== Wikitext Here ==
This is a fantastic slide!
|slideImage=File:Fruit.jpg|slideLink=PageName}}

Here are some important instructions regarding defining slides:

  • slideIndex must be 0 for the first slide, 1 for the second slide, etc. Numbers must be unique and incrementing from zero, and not doing this will result in slideshow display errors (but can be easily fixed by correcting the wikitext.)
  • slideCaption= can contain wikitext, such as headings and links. The best way to enter slideCaption is as above -- type a literal slideCaption=, followed by enter, then specify your wikitext, and terminate the caption by a single pipe character on the following line. Pipe characters are used to separate arguments from each other.
  • Specify your image name in the slideImage field. Your slideImage will have a name of File:myname.jpg, where myname.jpg is the Destination Filename you used when uploading the image.
  • An optional parameter called slideLink= can be provided to allow the image to be clickable and link to another wiki page. If it is omitted, then the image will not be clickable.

Add Slideshow to Page

Once the slides have been added to the page, you can add the following text to your page at the point you'd like the slideshow to appear:

{{Slideshow}}

YouTube Videos (Screencasts, etc.)

Screencasting is an easy method to explain complex tasks. Take for instance youtu.be/5KDei5mBfSg and chop off the id and insert it into the following syntax to produce a video example.

{{#widget:YouTube16x9|id=5KDei5mBfSg}}

Tip

The sample video above explains how to create your own screencasts under Funtoo Linux.

Most YouTube videos are in 16x9 format and should use the YouTube16x9 widget. There is also a YouTube4x3 widget for videos with a 4x3 aspect ratio.

Note

These YouTube widgets have been updated to be mobile-friendly.