rsync/support/rrsync.1.md

## NAME

rrsync - a script to setup restricted rsync users via ssh logins

## SYNOPSIS

```
rrsync [-ro|-wo] [-munge] [-no-del] [-no-lock] [-no-overwrite]  DIR
```

The single non-option argument specifies the restricted _DIR_ to use. It can be
relative to the user's home directory or an absolute path.

The online version of this manpage (that includes cross-linking of topics)
is available at <https://download.samba.org/pub/rsync/rrsync.1>.

## DESCRIPTION

A user's ssh login can be restricted to only allow the running of an rsync
transfer in one of two easy ways:

* forcing the running of the rrsync script
* forcing the running of an rsync daemon-over-ssh command.

Both of these setups use a feature of ssh that allows a command to be forced to
run instead of an interactive shell.  However, if the user's home shell is bash,
please see [BASH SECURITY ISSUE](#) for a potential issue.

To use the rrsync script, edit the user's `~/.ssh/authorized_keys` file and add
a prefix like one of the following (followed by a space) in front of each
ssh-key line that should be restricted:

> ```
> command="rrsync DIR"
> command="rrsync -ro DIR"
> command="rrsync -munge -no-del DIR"
> ```

Then, ensure that the rrsync script has your desired option restrictions. You
may want to copy the script to a local bin dir with a unique name if you want
to have multiple configurations. One or more rrsync options can be specified
prior to the _DIR_ if you want to further restrict the transfer.

To use an rsync daemon setup, edit the user's `~/.ssh/authorized_keys` file and
add a prefix like one of the following (followed by a space) in front of each
ssh-key line that should be restricted:

> ```
> command="rsync --server --daemon ."
> command="rsync --server --daemon --config=/PATH/TO/rsyncd.conf ."
> ```

Then, ensure that the rsyncd.conf file is created with one or more module names
with the appropriate path and option restrictions.  If rsync's
[`--config`](rsync.1#dopt) option is omitted, it defaults to `~/rsyncd.conf`.
See the [**rsyncd.conf**(5)](rsyncd.conf.5) manpage for details of how to
configure an rsync daemon.

When using rrsync, there can be just one restricted dir per authorized key.  A
daemon setup, on the other hand, allows multiple module names inside the config
file, each one with its own path setting.

The remainder of this manpage is dedicated to using the rrsync script.

## OPTIONS

0.  `-ro`

    Allow only reading from the DIR. Implies [`-no-del`](#opt) and
    [`-no-lock`](#opt).

0.  `-wo`

    Allow only writing to the DIR.

0.  `-munge`

    Enable rsync's [`--munge-links`](rsync.1#opt) on the server side.

0.  `-no-del`

    Disable rsync's `--delete*` and `--remove*` options.

0.  `-no-lock`

    Avoid the single-run (per-user) lock check.  Useful with [`-munge`](#opt).

0.  `-no-overwrite`

    Enforce `--ignore-existing` on the server. Prevents overwriting existing
    files when the server is the receiver.

0.  `-help`, `-h`

    Output this help message and exit.

## SECURITY RESTRICTIONS

The rrsync script validates the path arguments it is sent to try to restrict
them to staying within the specified DIR.

The rrsync script rejects rsync's [`--copy-links`](rsync.1#opt) option (by
default) so that a copy cannot dereference a symlink within the DIR to get to a
file outside the DIR.

The rrsync script rejects rsync's [`--protect-args`](rsync.1#opt) (`-s`) option
because it would allow options to be sent to the server-side that the script
cannot check.  If you want to support `--protect-args`, use a daemon-over-ssh
setup.

The rrsync script accepts just a subset of rsync's options that the real rsync
uses when running the server command.  A few extra convenience options are also
included to help it to interact with BackupPC and accept some convenient user
overrides.

The script (or a copy of it) can be manually edited if you want it to customize
the option handling.

## BASH SECURITY ISSUE

If your users have bash set as their home shell, bash may try to be overly
helpful and ensure that the user's login bashrc files are run prior to
executing the forced command.  This can be a problem if the user can somehow
update their home bashrc files, perhaps via the restricted copy, a shared home
directory, or something similar.

One simple way to avoid the issue is to switch the user to a simpler shell,
such as dash.  When choosing the new home shell, make sure that you're not
choosing bash in disguise, as it is unclear if it avoids the security issue.

Another potential fix is to ensure that the user's home directory is not a
shared mount and that they have no means of copying files outside of their
restricted directories.  This may require you to force the enabling of symlink
munging on the server side.

A future version of openssh may have a change to the handling of forced
commands that allows it to avoid using the user's home shell.

## EXAMPLES

The `~/.ssh/authorized_keys` file might have lines in it like this:

> ```
> command="rrsync client/logs" ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAzG...
> command="rrsync -ro results" ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAmk...
> ```

## FILES

~/.ssh/authorized_keys

## SEE ALSO

[**rsync**(1)](rsync.1), [**rsyncd.conf**(5)](rsyncd.conf.5)

## VERSION

This manpage is current for version @VERSION@ of rsync.

## CREDITS

rsync is distributed under the GNU General Public License.  See the file
[COPYING](COPYING) for details.

An rsync web site is available at <https://rsync.samba.org/> and its github
project is <https://github.com/RsyncProject/rsync>.

## AUTHOR

The original rrsync perl script was written by Joe Smith.  Many people have
later contributed to it.  The python version was created by Wayne Davison.