Difference between pages "User:Jeanfrancis" and "SFTP Only Access"

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{{Person
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= Context =
|Full name=Jean-Francis Roy
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|Email=jeanfrancis@funtoo.org
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|Nick=jeanfrancis
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|Geoloc=46.8032826, -71.242796
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|Location name=Québec City, Québec, Canada
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|Roles={{Role
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|Role type=Staff
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|Role desc=Core Team member
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|Start date=2011/11/01
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}}
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|Maintains=
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|Blogs=
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}}
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I'm a Computer Science Ph.D. candidate at Université Laval, Canada. I'm interested in Machine Learning, and more specifically in Semi-Supervised Learning.
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See my webpage[http://jeanfrancisroy.com] for more info!
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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>
 +
Subsystem      sftp    /usr/lib64/misc/sftp-server
 +
</pre>
 +
 
 +
and change it for:
 +
 
 +
<pre>
 +
Subsystem      sftp    internal-sftp
 +
</pre>
 +
 
 +
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:
 +
 
 +
<pre>
 +
# Restricted users, no TCP connexions bouncing, no X tunneling.
 +
Match group sftponly
 +
        ChrootDirectory /home/%u
 +
        X11Forwarding no
 +
        AllowTcpForwarding no
 +
        ForceCommand internal-sftp
 +
</pre>
 +
 
 +
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
 +
 
 +
[[Category:HOWTO]]

Revision as of 16:50, August 30, 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