Difference between pages "Initramfs" and "Hostname"

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== What is initramfs? ==
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==Introduction==
Wikipedia defines initramfs as:
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A hostname is a unique name created to identify a machine on a network. In computer networking, a hostname  is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet. Hostnames may be simple names consisting of a single word or phrase, or they may be structured.
<blockquote>
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==Configuration==
initramfs, abbreviated from "initial ram file system", is the successor of initrd. It is a cpio archive of the initial file system that gets loaded into memory during the Linux startup process. The Linux kernel mounts it as root file system and starts the init process from it. This will complete certain tasks before the real root file system is loaded; thus, initramfs needs to contain all of the device drivers and tools needed to mount the real root filesystem.
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In Funtoo Linux <code>/etc/conf.d/hostname</code> is the only configuration file for setting a hostname. In OpenRC framework <code>/etc/conf.d/foo</code> is the configuration file for a corresponding Init script <code>/etc/init.d/foo</code>.  With the case of hostname, default value in <code>/etc/conf.d/hostname</code> is set to ''localhost'', means when system boots and OpenRC's <code>/etc/init.d/hostname</code> script started a hostname getting only ''localhost'' name.  How it looks?  In your shell promt this will look in following way, an example for root:
</blockquote>
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<console>
[[Category:Kernel]]
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localhost ~ # ##i## Hello :)
 +
</console>
 +
Let's play a bit with a configuration. Open <code>/etc/conf.d/hostname</code> with your favorite editor and set a hostname of your choice.  Below, I will use a real examples  from one of my working test boxes.
 +
<console>
 +
localhost ~ # ##i## nano /etc/conf.d/hostname
 +
</console>
 +
Let's set it to hostname="oleg-stable.host.funtoo.org". Save the file and restart  a hostname service:
 +
<console>
 +
localhost ~ # ##i## service hostname restart
 +
</console>
 +
Now, let's examine our changes, after a restarting a hostname
 +
<console>
 +
oleg-stable ~ # ##i## Hello :)
 +
</console>
 +
== Diving deeper==
 +
Notice, that in above output we seeing a shortened hostname and not a FQDN (Fully Qualified Domain Name). Don't be frustrated. This is how  default bash promt <code>PS1</code> set. To get nice promts, please, follow http://www.funtoo.org/Prompt_Magic
 +
Another way to test our settings is using a '''hostname''' command. Here we will show only  some of it's features. Let's try to execute '''hostname''' command:
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<console>
 +
oleg-stable ~ # ##i## hostname
 +
oleg-stable.host.funtoo.org
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</console>
 +
Now we see our fully qualified domain name hostname just how we configured it in <code>/etc/conf.d/hostname</code> in above paragraph. To get a short hostname we need to set '''-s ''' (short) argument to hostname command.
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<console>
 +
oleg-stable ~ # ##i## hostname -s
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oleg-stable
 +
</console>
 +
Good! Hostname offers more then just displaying a system host name but can also set one. Let's try:
 +
<console>
 +
oleg-stable ~ # ##i## hostname foo.bar.baz
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oleg-stable ~ # ##i## hostname
 +
foo.bar.baz
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</console>
 +
As you can see, we changed a hostname on-the-fly. This is not recommended way.
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{{fancywarning|Please, notice that using '''hostname''' command to configure will work temporary for a current session and will be reverted back to a value set in <code>/etc/conf.d/hostname</code> file with next system restart.}}
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Now that we got a brief description of a hostname and basic configuration steps, its time to reflect another important case which is directly related to a Funtoo Linux hostname generation, a hosts.
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 +
==Hosts case==
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As per man page <code>hosts</code> stands for static table lookup for hostnames and it's configuration file is <code>/etc/hosts</code>. Here is how it looks
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{{file|name=/etc/hosts|body=
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# Auto-generated hostname. Please do not remove this comment.
 +
127.0.0.1      oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
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::1            oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
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}}
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As you can see it has entries from our <code>/etc/conf.d/hostname</code>. As you may have guessed, in Funtoo Linux <code>/etc/hosts</code> file entries are auto-generated, when OpenRC hostname service starts. Previously, it is used to edit <code>/etc/hosts</code> manually. In Funtoo Linux there is no such need.
 +
 
 +
What about custom hosts entries? This can be easily configured with 'aliases'. For example you want to have a hosts for your remote router or a computer in home LAN. Let's try to modify <code>/etc/conf.d/hostname</code> with adding following - my remote computer oleg.distant.home has an IP 10.1.1.2:
 +
<console>
 +
oleg-stable ~ # ##i## echo 'aliases="10.1.12 oleg.distant.home"' >> /etc/conf.d/hostname
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oleg-stable ~ # ##i## service hostname restart
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</console>
 +
Examine our changes:
 +
<console>
 +
oleg-stable ~ # ##i## cat /etc/hosts
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</console>
 +
{{file|name=/etc/hosts|body=
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# Auto-generated hostname. Please do not remove this comment.
 +
10.1.1.2        oleg.distant.home
 +
127.0.0.1      oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
 +
::1            oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
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}}

Revision as of 16:06, February 24, 2015

Introduction

A hostname is a unique name created to identify a machine on a network. In computer networking, a hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet. Hostnames may be simple names consisting of a single word or phrase, or they may be structured.

Configuration

In Funtoo Linux /etc/conf.d/hostname is the only configuration file for setting a hostname. In OpenRC framework /etc/conf.d/foo is the configuration file for a corresponding Init script /etc/init.d/foo. With the case of hostname, default value in /etc/conf.d/hostname is set to localhost, means when system boots and OpenRC's /etc/init.d/hostname script started a hostname getting only localhost name. How it looks? In your shell promt this will look in following way, an example for root:

localhost ~ #  Hello :)

Let's play a bit with a configuration. Open /etc/conf.d/hostname with your favorite editor and set a hostname of your choice. Below, I will use a real examples from one of my working test boxes.

localhost ~ #  nano /etc/conf.d/hostname

Let's set it to hostname="oleg-stable.host.funtoo.org". Save the file and restart a hostname service:

localhost ~ #  service hostname restart

Now, let's examine our changes, after a restarting a hostname

oleg-stable ~ #  Hello :)

Diving deeper

Notice, that in above output we seeing a shortened hostname and not a FQDN (Fully Qualified Domain Name). Don't be frustrated. This is how default bash promt PS1 set. To get nice promts, please, follow http://www.funtoo.org/Prompt_Magic Another way to test our settings is using a hostname command. Here we will show only some of it's features. Let's try to execute hostname command:

oleg-stable ~ #  hostname
oleg-stable.host.funtoo.org

Now we see our fully qualified domain name hostname just how we configured it in /etc/conf.d/hostname in above paragraph. To get a short hostname we need to set -s (short) argument to hostname command.

oleg-stable ~ #  hostname -s
oleg-stable

Good! Hostname offers more then just displaying a system host name but can also set one. Let's try:

oleg-stable ~ #  hostname foo.bar.baz
oleg-stable ~ #  hostname 
foo.bar.baz

As you can see, we changed a hostname on-the-fly. This is not recommended way.

Warning

Please, notice that using hostname command to configure will work temporary for a current session and will be reverted back to a value set in /etc/conf.d/hostname file with next system restart.

Now that we got a brief description of a hostname and basic configuration steps, its time to reflect another important case which is directly related to a Funtoo Linux hostname generation, a hosts.

Hosts case

As per man page hosts stands for static table lookup for hostnames and it's configuration file is /etc/hosts. Here is how it looks

/etc/hosts
# Auto-generated hostname. Please do not remove this comment.
127.0.0.1       oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
::1             oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain

As you can see it has entries from our /etc/conf.d/hostname. As you may have guessed, in Funtoo Linux /etc/hosts file entries are auto-generated, when OpenRC hostname service starts. Previously, it is used to edit /etc/hosts manually. In Funtoo Linux there is no such need.

What about custom hosts entries? This can be easily configured with 'aliases'. For example you want to have a hosts for your remote router or a computer in home LAN. Let's try to modify /etc/conf.d/hostname with adding following - my remote computer oleg.distant.home has an IP 10.1.1.2:

oleg-stable ~ #  echo 'aliases="10.1.12 oleg.distant.home"' >> /etc/conf.d/hostname
oleg-stable ~ #  service hostname restart
Examine our changes:
oleg-stable ~ #  cat /etc/hosts
/etc/hosts
# Auto-generated hostname. Please do not remove this comment.
10.1.1.2        oleg.distant.home
127.0.0.1       oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain
::1             oleg-stable.host.funtoo.org oleg-stable localhost localhost.localdomain