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Dohn Joe
Asked: 2024-02-15 03:13:15 +0800 CST

sshfs fails when not used with sudo

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I changed computers, and now I have trouble getting sshfs to work again.

Using the command sshfs user@server:/home/user/ /mnt/server fails with an:
fusermount3: mount failed: Operation not permitted.
When I run the command with a preceeding sudo, it works - but that's somewhat beside the point. This used to work without using sudo.

This used to work on my older machine, which was also running Ubuntu 22.04. However, it's been a while since I set the old machine up, so I guess I may have forgotten something.

The mount-directory /mnt/server belongs to my current user, both as owner and with the group.

Simply logging in using ssh works, i.e., using ssh user@server. So, what is the operation that is not permitted?

The mount-point looks as follows:

user@host:~$ ls -ld /mnt/server
drwxr-xr-x 2 user user 4096 Jän 16 17:30 /mnt/server
user@host:~$

Further info:

user@host:~$ type -a fusermount3 
fusermount3 ist /usr/bin/fusermount3
fusermount3 ist /bin/fusermount3
user@host:~$ ls -l /usr/bin/fusermount3 
-rwxr-xr-x 1 root root 35200 Mär 23  2022 /usr/bin/fusermount3

I tried it on a different computer, also running Ubuntu-22.04, and I noticed some differences in the groups, that the local user is a member of:

user@host:~$ id
uid=1003(user) gid=1003(user) Gruppen=1003(user),27(sudo),46(plugdev)

user@otherHost:~$ id
uid=1000(user) gid=1000(user) Gruppen=1000(user),4(adm),27(sudo),30(dip),46(plugdev),122(lpadmin),134(lxd),135(sambashare)

With host being the computer, where it's not working; and otherHost being the other computer where it works.

22.04

1 Answers

  1. Best Answer

    Your:

    $ ls -l /usr/bin/fusermount3 
-rwxr-xr-x 1 root root 35200 Mär 23  2022 /usr/bin/fusermount3

    ... is missing the set-user-ID bit while it should be there by default for non-admin users to be able to use that command for mounting a filesystem ... That bit when set will run the command as the owner user i.e. root regardless of the invoking user/process or else the command will run as the invoking user instead and you will need to either be root or use sudo as you have experienced.

    Run:

    sudo chmod u+s /usr/bin/fusermount3

    ... to set that bit so it will look like this:

    $ ls -l /usr/bin/fusermount3 
-rwsr-xr-x 1 root root 35200 Mär 23  2022 /usr/bin/fusermount3

    ... and then try your command again and it should work.

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