Parameter ChrootDirectory in /etc/ssh/sshd_config allows the specification of a chroot target directory which will then be used for all ssh and sftp sessions to this server. The target directory definition can utilize the %u and %h tokens to customize the target directory based on the username or the users home directory. Below are various scenarious and their configuration steps.
Dec 17, 2020 ssh is a client program for logging into a remote machine and for executing commands on a remote Linux or Unix computer. SSHD is the daemon program for ssh. Bots and unwanted people often target SSHD. Hence, you must protect your server. Open SSH port using ufw. The syntax is as follows to open ssh port using ufw command: sudo ufw allow ssh OR. Chrooting the ssh users, by properly configuring the ssh daemon you can ask it to chroot a user after authentication just before it is provided a shell. Each user can have their own environment. Chrooting the ssh server, since you chroot the ssh application itself all users are chrooted to the defined environment. Create a chroot environment directory named /data/chroot-ssh. You can create the chroot environment directory on any path of your choice. Create a chroot group named chrootssh. You can create the chroot group of your choice. As far as I know new versions of OpenSSH only allows chroot for SFTP connections. I tried and it works. But for SSH the solution available is the chrootssh patch. I browse the SourceForge site and there are no files so I think is discontinued.
Case 1 : One common chroot directory for all users
In this example we will configure one target directory which will be used for all users. This is the simplest setup. We will use the directory /export/home/chroot in this example.
1. Create the chroot area by using the ftpconfig command:
2. Create the user and assign a password:
3. Add the following chroot option to the file /etc/ssh/sshd_config
4. Restart the ssh service to activate the configuration changes:
Case 2 : One common chroot directory for all users, but each user has its own home directory inside this area
In this example we will configure one target directory which will be used for chroot but each user has its own home directory inside this area. After a login the user will find himself inside the home directory but can still navigate inside the entire chroot area. The user is therefore not restricted to his own home directory. We will use /export/home/chroot as the common chroot directory.
1. Create the chroot area by using the ftpconfig command:
2. Create the user with its own home directory inside the chroot area and assign a password to the user:
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3. Change the users home directory to make it valid and relative inside the chroot area. Different types of post office jobs. In this example it would be /testuser
4. Add the following chroot option to the file /etc/ssh/sshd_config file.
Mac webcam presentation software. 5. Restart the ssh service to activate the configuration change:
Case 3 : Each user has a separate chroot environment
In this example we will setup an individual chroot area for each user. Please note that this needs more disk space than the first two options as each area needs to be populated with a few required files. We will setup the user home directories under /export/home/chroot where each user will have its own full populated environment.
1. Create the target chroot environment by using the ftpconfig command:
2. Create the user and assign a password:
3. Add the following chroot configuration line to the file /etc/ssh/sshd_config: Tekkit minecraft download mac.
4. Restart the ssh service to activate the configuration change:
Note: You can also use the target directory /export/home/chroot/%u in the ChrootDirectory definition above
You may have seen the recent commit message from djm@ about the new feature in OpenSSH: ChrootDirectory
Damien Miller (djm@), who worked on this new feature with Markus Friedl (markus@), offers more details about ChrootDirectory:
This commit adds a chroot(2) facility to sshd, controlled by a new sshd_config(5) option 'ChrootDirectory'. This can be used to 'jail' users into a limited view of the filesystem, such as their home directory, rather than letting them see the full filesystem.
More from Damien follows.
Unfortunately, setting up a chroot(2) environment is complicated, fragile and annoying to maintain. The most frequent reason our users have given when asking for chroot support in sshd is so they can set up file servers that limit semi-trusted users to be able to access certain files only. Because of this, we have made this particular case very easy to configure.
In a previous commit, markus@ implemented an 'in-process' sftp server in sshd, basically linking sftp-server(8) into sshd(8). When the in-process sftp server is used, sshd does not need any special chroot configuration (no /dev nodes, no libraries, no statically-linked sftp-server) so the chroot setup and maintenance burden is eliminated. The chroot support does work for login and command-execution sessions too, but administrators will need to configure the chroot environment manually.
To set up a restricted sftp server one should use the 'ForceCommand' and 'ChrootDirectory' directives in sshd_config. Presumably most people will not want to restrict every user, so they should also use the 'Match' directive to select a user or group to apply the restrictions to. For example:
This will cause the user 'djm' to be chrooted to the '/chroot' directory at login, and the use of the in-process sftp server will be forced for all connections. I.e. the user will not be able to login interactively, or run arbitrary commands - the login will only be useful for sftp transfers. Note that the user's home directory may exist under the '/chroot' directory above (e.g. '/chroot/home/djm') and sshd will try to chdir to it before starting to serve files, but it doesn't matter if it does not exist.
Setting up a safe chroot jail is somewhat tricky, and it is quite easy to make to compromise one's security. To reduce this risk, sshd ensures the ChrootDirectory and each of its components is root-owned and not writable by other users, but it is still possible for administrators to break their own setups by doing dumb things (e.g. leaving /dev nodes for the physical drives in a chroot, executing scripts inside the chroot from cron(8) or elsewhere, etc.).
Sftp Chroot Configuration In Linux
A limitation of the chroot support is that the in-process sftp server does not support scp(1) transfers. scp is a really busted protocol and it would be a fair bit more work to build it in in the way we have built in sftp. It is still possible to support chrooted scp, but administrators will need to populate the chroot environment manually. Please use sftp instead.
To make the internal-sftp chroot work for me, I made the following changes to /etc/ssh/sshd_config:
Sftp Chroot
The full commit message:
Ssh Chroot Sftp
Thanks to Damien Miller for taking the time to explain the ChrootDirectory feature.