Difference between pages "Template:Shell/Doc" and "SFTP Only Access"

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Example 1:
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= Context =
 +
 
 +
In some cases, it can be useful to set up an access on your Funtoo box such as a user:
 +
* does not see the whole contents of the machine but, instead, remains "jailed" in a home directory
 +
* is able to transfer files back and forth on the box via SFTP
 +
* does not have access to a shell
 +
 
 +
Such a SFTP only access is easy to setup:
 +
 
 +
# Assign a group (e.g. ''sftponly'') to users that must be restricted to a SFTP-only account
 +
# Change a bit the configuration of OpenSSH so that users belonging to your sftp-only group are given a chrooted access
 +
# Make OpenSSH ignore any other command than running sftp-server on the server side for users belonging to your sftp-only group (this is where the trick lies !)
 +
 
 +
= Quick start =
 +
 
 +
First, a dedicated group must be created. For the sake of the example we use sftponly here, use whatever name fits your preferences:
 +
 
 +
<pre>
 +
# groupadd sftponly
 +
</pre>
 +
 
 +
Next in the configuration of OpenSSH (located in '''/etc/sshd/sshd_config''') locate:
 +
 
 
<pre>
 
<pre>
{{shell
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Subsystem      sftp    /usr/lib64/misc/sftp-server
| Desc = Descriptiontext
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| Input = # command to run
+
Output of command<br>
+
<font color=#ff0000;>Alert!</font>
+
}}
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</pre>
 
</pre>
  
Will produce:
+
and change it for:
{{shell
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| Desc = Descriptiontext
+
| Input = # command to run
+
Output of command<br>
+
<font color=#ff0000;>Alert!</font>
+
}}
+
  
and Example 2:
 
 
<pre>
 
<pre>
{{shell
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Subsystem      sftp    internal-sftp
| Input = # command to run
+
Output of command<br>
+
<font color=#ff0000;>Alert!</font>
+
}}
+
 
</pre>
 
</pre>
  
Will produce:
+
Now the $100 question: ''"how can OpenSSH can be told to restrict a user access to a simple sftp session?"'' Simple! Assuming that ''sftponly'' is the group you use for for your restricted users, just add to the file '''/etc/sshd/sshd_config''' the following statement:
{{shell
+
| Input = # command to run
+
Output of command<br>
+
<font color=#ff0000;>Alert!</font>
+
}}
+
  
and Example 3:
 
 
<pre>
 
<pre>
{{shell
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# Restricted users, no TCP connexions bouncing, no X tunneling.
| Desc =
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Match group sftponly
| Input = # command to run
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        ChrootDirectory /home/%u
Output of command<br>
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        X11Forwarding no
<font color=#ff0000;>Alert!</font>
+
        AllowTcpForwarding no
}}
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        ForceCommand internal-sftp
 
</pre>
 
</pre>
  
Will produce:
+
To understand how it works, you must be aware that, when you open an SSH session, the SSHD process launch a process on the server side which could be:
{{shell
+
* a shell => ssh login@host
| Desc =
+
* a kind of dedicated ftp daemon (sftp-server) => sftp user@host
| Input = # command to run
+
Output of command<br>
+
<font color=#ff0000;>Alert!</font>
+
}}
+
  
Please be aware if you are using | inside the Input String it wouldn't work and break you need to replace | with {{!}} and inside the input it is saver to use clean HTML code. :)
+
TBC
  
<noinclude>[[Category:Template Documentation]]</noinclude>
+
[[Category:HOWTO]]

Revision as of 16:50, 30 August 2011

Context

In some cases, it can be useful to set up an access on your Funtoo box such as a user:

  • does not see the whole contents of the machine but, instead, remains "jailed" in a home directory
  • is able to transfer files back and forth on the box via SFTP
  • does not have access to a shell

Such a SFTP only access is easy to setup:

  1. Assign a group (e.g. sftponly) to users that must be restricted to a SFTP-only account
  2. Change a bit the configuration of OpenSSH so that users belonging to your sftp-only group are given a chrooted access
  3. Make OpenSSH ignore any other command than running sftp-server on the server side for users belonging to your sftp-only group (this is where the trick lies !)

Quick start

First, a dedicated group must be created. For the sake of the example we use sftponly here, use whatever name fits your preferences:

# groupadd sftponly

Next in the configuration of OpenSSH (located in /etc/sshd/sshd_config) locate:

Subsystem      sftp    /usr/lib64/misc/sftp-server

and change it for:

Subsystem      sftp    internal-sftp

Now the $100 question: "how can OpenSSH can be told to restrict a user access to a simple sftp session?" Simple! Assuming that sftponly is the group you use for for your restricted users, just add to the file /etc/sshd/sshd_config the following statement:

# Restricted users, no TCP connexions bouncing, no X tunneling.
Match group sftponly
        ChrootDirectory /home/%u
        X11Forwarding no
        AllowTcpForwarding no
        ForceCommand internal-sftp

To understand how it works, you must be aware that, when you open an SSH session, the SSHD process launch a process on the server side which could be:

  • a shell => ssh login@host
  • a kind of dedicated ftp daemon (sftp-server) => sftp user@host

TBC