Arch Linux

kde35

Member

Registered: 2015-04-13

Posts: 71

su: Authentication failure [Solved]

Hi, on a freshly installed Archlinux machine, I can log in as a root, but I can't su from a normal user.  That is, I get the error

$ su
Password: 
su: Authentication failure

Although the password is correct.

Actually, I can't even su from a normal account to itself!  That is,

[tk@rudolph ~]$ su tk
Password: 
su: Authentication failure

And the journalctl says

déc. 18 17:22:18 rudolph unix_chkpwd[1129]: check pass; user unknown
déc. 18 17:22:18 rudolph unix_chkpwd[1129]: password check failed for user (tk)
déc. 18 17:22:18 rudolph su[1128]: pam_unix(su:auth): authentication failure; logname=tk uid=1000 euid=1000 tty=pts/0 ruser=tk rhost=  user=tk
déc. 18 17:22:20 rudolph su[1128]: FAILED SU (to tk) tk on pts/0

(I am aware of the thread telling us to post a complete output of a command, but the complete output of journalctl would take several pages, so I took the liberty of posting just these lines).

I have seen this thread and this one, but
there certainly is not the problem of suid

$ ls -l /usr/bin/su
-rwsr-xr-x 1 root root 31744  7 nov.  18:10 /usr/bin/su

And, as to the second thread, I checked everything that is said there, and updating root's password didn't help.  The /etc/pam.d/su and  /etc/pam.d/su-l files are just as they are supposed to be (I have another
machine running Archlinux on which su works correctly, and the files are identical).   The version of  util-linux is the latest one (2.28.2-2). 

Any idea on what is going wrong?

Last edited by kde35 (2016-12-18 17:05:28)

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,538

Re: su: Authentication failure [Solved]

Just as an experiment, what happens if you try sudo su   ? Note that the password you will need is your user password, not the root password (Assuming, of course, you have set up sudo and your user is a member of wheel)

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kde35

Member

Registered: 2015-04-13

Posts: 71

Re: su: Authentication failure [Solved]

Great! This solves the problem...

 sudo su
sudo: effective uid is not 0, is /usr/bin/sudo on a file system with the 'nosuid' option set or an NFS file system without root privileges?

And, of course, according to  /etc/fstab, the root partition is mounted with the nosuid option.  So all I need to do now is to edit the fstab and reboot.  Thank you very much.