SCP 与 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)[编辑 | 编辑源代码]
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[编辑 | 编辑源代码]
Sysadmins can jail a subset of users to a chroot jail using openssh包 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包 to put/get files in the chroot jail.
Setup the filesystem[编辑 | 编辑源代码]
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
/etc/fstab
to make the bind mount survive a reboot.Create an unprivileged user[编辑 | 编辑源代码]
Create the share user and setup a good password:
# useradd -g sshusers -d /var/lib/jail foo # passwd foo
Setup OpenSSH[编辑 | 编辑源代码]
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 configuration file. See SFTP chroot to configure the keys correctly when using chroot or it will get permission denied.
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)[编辑 | 编辑源代码]
Install, configure and start OpenSSH. It contains the scp utility to transfer files.
More features are available by installing additional packages, for example rsshAUR or scponly包 described below.
-O
option must be used to use the legacy SCP protocol.General Usage[编辑 | 编辑源代码]
Linux to Linux[编辑 | 编辑源代码]
Copy file from a remote host to local host SCP example:
$ scp username@from_host:file.txt /local/directory/
Copy file from local host to a remote host SCP example:
$ scp file.txt username@to_host:/remote/directory/
Copy directory from a remote host to local host SCP example:
$ scp -r username@from_host:/remote/directory/ /local/directory/
Copy directory from local host to a remote host SCP example:
$ scp -r /local/directory/ username@to_host:/remote/directory/
Copy file from remote host to remote host SCP example:
$ scp username@from_host:/remote/directory/file.txt username@to_host:/remote/directory/
Linux to Windows[编辑 | 编辑源代码]
Use a Windows program such as WinSCP
Scponly[编辑 | 编辑源代码]
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.
For existing users, simply set the user's shell to scponly:
# usermod -s /usr/bin/scponly username
Adding a chroot jail[编辑 | 编辑源代码]
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
hasroot:root
owner andr-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.
Uploads to Chroot jail root dir[编辑 | 编辑源代码]
For security reasons the directory set as the chroot directory must be owned by root with only root having write access to it otherwise sftp/ssh connections will be denied. This of course means regular users cannot upload files to the root directory. In order to get around this while not compromising security you can create a folder inside the chroot directory which the regular user or group has write access to, e.g:
# cd /var/lib/jail # mkdir uploads # chown :sshusers uploads # chmod 730 uploads
chmod 770
to allow sshusers to view contents.Some applications utilizing SFTP do not allow input of sub-directories when performing operations (e.g. uploading files), and will attempt to upload files to the chroot base directory (which will be denied). In order to force these applications to use a specific sub-directory you can append the following to the "ForceCommand" option:
/etc/ssh/sshd_config
... Match group sshusers ... ForceCommand internal-sftp -d /uploads
Users on connect will then have their start directory change to the specified sub-directory (remember to restart the sshd server).