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How can I prevent users accessing anything but their own home directory?

For example, I have a NTFS partition mounted under /media/ntfs, so if the user logs in through ssh he can reach this partition. How can I disable the users to cd out from their home directory?

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Reassess your requirement first. What is the problem you are trying to solve? Why do you want to prevent users from leaving their home directory? Isn't it rather that you don't want them to rummage through specific other directories -- such as the home directories of other users?

It is very difficult to prevent users from leaving their home directory. It is actually a bit silly, too (explanation follows). It is much simpler to prevent users from entering directories you don't want them to enter.

First off, yes you can give users a so-called restricted shell, see man rbash. This will prevent them from cd-ing elsewhere, but only inside that shell. If the user starts vi or nano (or any other program capable of opening a file) they can again open files anywhere on the system. As a matter of fact, a restricted shell does not prevent e.g. cat /etc/passwd.

The next step up is a root jail. More info on the community wiki and in this question. Though a root jail will lock users inside a walled garden, within which they have access to nothing but the files and commands that you intentionally put there, root jails really are intended for isolating untrusted software rather than users. In particular, they are for software that needs to run with elevated privileges -- hence a root jail.

Users, on the other hand, are trusted: they have had to authenticate and run without elevated privileges. Therefore file permissions suffice to keep them from changing files they do not own, and from seeing things they must not see. To prevent users from reading the content of a file, remove its world-readability with chmod o-r FILE . To keep users out of a directory, make it world-inaccessible with chmod o-rwx DIR.

World-readability is the default though, for good reason: users actually need most of the stuff that's on the file system. Don't lock users in their homes just because there exist secrets outside.

Why locking users in their home directory is a bit silly

To do anything useful, users need access to commands and applications. These are in directories like /bin and /usr/bin, so unless you copy all commands they need from there to their home directories, users will need access to /bin and /usr/bin. But that's only the start. Applications need libraries from /usr/lib and /lib, which in turn need access to system resources, which are in /dev, and to configuration files in /etc and /usr/share.

This was just the read-only part. Applications will also want /tmp and often /var to write into. So, if you want to constrain a user within his home directory, you are going to have to copy a lot into it. In fact, pretty much an entire base file system -- which you already have, located at /.

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    This doesn't make sense to me, there could be so many reasons why you would want a user to only have access to 1 folder. One example could be giving access for the sake of transmitting files from 1 server to another. I rather think that it's a bit silly that any user can browse the full system instead. – Richard Mar 28 '18 at 14:51
  • In my case I am setting up a user to allow devices to reverse ssh into the machine for remote management of devices. So I want to limit that user account as much as possible just in case it's compromised - I just need the successful connection to be made. I wouldn't say it's silly, it just depends on what you are trying to accomplish. – John Dec 9 '18 at 13:50
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I needed to provide access to user sam on /var/xyz only and block listing contents of other folders inside /var/

I used the following sequence of commands:

setfacl -R -m user:sam:--- /var/

setfacl -m user:sam:rx /var/

setfacl -R -m user:sam:rwx /var/xyz/

So the user can see directories listed under /var/ but cannot see contents under sub directories except /var/xyz.

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    Welcome to askubuntu! I don't see this as an answer to the question asked regarding home directories. – Elder Geek Jan 29 '15 at 21:57
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    @ElderGeek Can't the OP just use the same commands, but for the home directory? – Seth Jan 30 '15 at 4:25
  • @Seth Yes, but would that be clear to the average user? – Elder Geek Jan 30 '15 at 14:39
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    @Elder Yes, I believe it would. Not perfect, but still an answer – Seth Jan 30 '15 at 16:43
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In addition to restricting access to other directories, particularly other users' home directories, I also didn't want a user to ll /home and see the names of the other users on the system.

To prevent this, as root run chmod 701 /home. This makes the /home directory itself "read/write/execute" to root of course, but only "execute" to everyone else. /home is still accessible to cd to, but users cannot read its contents- the other users' home folders and therefore usernames.

  • This, although not strictly an answer to the question, is still very interesting... In a situation where you operate a remote server that clients can ssh in to, this is great. They can still move around as they'd expect, whilst retaining the privacy of other clients usernames. – Jack_Hu Jun 1 '18 at 19:12

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