SCP and SFTP - ArchWiki

# SCP and SFTP

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Related articles

- SSHFS
- SFTP chroot
- Pure-FTPd

This article or section is a candidate for merging with SFTP chroot.

Notes: Instructions seem to be the same as in SFTP chroot and has more content. (Discuss in Talk:SCP and SFTP#)

The Secure copy (SCP) is a protocol to transfer files via a Secure Shell connection. The SSH file transfer protocol (SFTP) is a related protocol, also relying on a secure shell back-end. Both protocols allow secure file transfers, encrypting passwords and transferred data. The SFTP protocol, however, features additional capabilities like, for example, resuming broken transfers or remote file manipulation like deletion.

## Secure file transfer protocol (SFTP)

Install and configure OpenSSH. Once running, SFTP is available by default.

Access files with the sftp program or SSHFS. Many standard FTP programs should work as well.

## Secure file transfer protocol (SFTP) with a chroot jail

Sysadmins can jail a subset of users to a chroot jail using openssh thus restricting their access to a particular directory tree. This can be useful to simply share some files without granting full system access or shell access. Users with this type of setup may use SFTP clients such as filezilla to put/get files in the chroot jail.

### Setup the filesystem

Create a jail directory:

    # mkdir -p /var/lib/jail

Optionally, bind mount the filesystem to be shared to this directory. In this example, `/mnt/data/share` is to be used. It is owned by root and has octal permissions of 755.

    # mount -o bind /mnt/data/share /var/lib/jail

Tip: Consider adding an entry to `/etc/fstab` to make the bind mount survive a reboot.

### Create an unprivileged user

Create the share user and setup a good password:

    # useradd -g sshusers -d /var/lib/jail foo
    # passwd foo

### Setup openssh

Add the following to the end of `/etc/ssh/sshd_config` to enable the share and to enforce the restrictions:

    /etc/ssh/sshd_config

    ...
     Match group sshusers
      ChrootDirectory %h
      X11Forwarding no
      AllowTcpForwarding no
      PasswordAuthentication yes
      ForceCommand internal-sftp

Restart `sshd.service` to re-read the config file.

Test that in fact, the restrictions are enforced by attempting an ssh connection via the shell. The ssh server should return a polite notice of the setup:

    $ ssh foo@someserver.com
    foo@someserver.com's password:
    This service allows sftp connections only.
    Connection to someserver.com closed.

## Secure copy protocol (SCP)

Install, configure and start openssh. It contains a scp command to transfer files. See Secure Shell for more information.

More features are available by installing additional packages, for example rsshAUR or scponly described below.

### Scponly

Scponly is a limited shell for allowing users scp/sftp access and only scp/sftp access. Additionally, one can setup scponly to chroot the user into a particular directory increasing the level of security.

install scponly.

For existing users, simply set the user's shell to scponly:

    # usermod -s /usr/bin/scponly username

#### Adding a chroot jail

The package comes with a script to create a chroot. To use it, run:

    # /usr/share/doc/scponly/setup_chroot.sh

- Provide answers
- Check that `/path/to/chroot` has `root:root` owner and `r-x` for others
- Change the shell for selected user to `/usr/bin/scponlyc`
- sftp-server may require some libnss modules such as libnss_files. Copy them to chroot's `/lib` path.

Categories:

- Secure Shell
- File Transfer Protocol

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