Well, for an unknown reason the file /etc/group has been cleared during a ssh session last week. As I manage ssh with allowgroups sshusers I could no more log in, but could however use the current session to modify sshd_config with allowusers so I can still log in.

I first though the problem came from command sudo addgroup user group I entered instead of sudo adduser user group, because group was void just after this. But after retrying it seems both commands are equivalent. So to be completely honnest, /etc/group is not void but contains only the last created groups. After those commands :

$ sudo adduser crashdebug 
$ sudo adduser helloworld testing
$ sudo addgroup helloworld testing
$ sudo deluser helloworld testing

I got this (first line is blank) :

$ sudo cat /etc/group


And :

$ groups pi && groups crashdebug && groups helloworld
pi : crashdebug
crashdebug : crashdebug
helloworld : groups: cannot find name for group ID 1004
1004 testing
$ id pi && id crashdebug && id helloworld
uid=1000(pi) gid=1000(crashdebug) groups=1000(crashdebug)
uid=1005(crashdebug) gid=1000(crashdebug) groups=1000(crashdebug)
uid=1004(helloworld) gid=1004 groups=1004,1001(testing)
$ getent group

Some of /etc/passwd including all created users :

$ cat /etc/passwd |  grep /bin/bash

I have no idea what is going on here. Maybe the problem is sd card corruption because /etc/group- is filled with binary dump and /var/log/auth.log to a great extent too. Anyway, apart the above problems, the Raspberry still works without much issues, though I would not dare to restart it. User pi is still sudoer, though it belongs only to group crashdebug which is not sudoer (tested), even after re-logging/re-sshing pi is still sudoer, how is it possible ???

Has anybody any idea how to address this issue ?

  • Can you show some of your /etc/passwd that includes them? – SDsolar Jun 12 '18 at 3:58
  • 5
    You seem to have two choices. 1) live with the uncertainty of not knowing when you might lose important data, or 2) re-flash the SD card and be more careful in future. – joan Jun 12 '18 at 10:00
  • @Joan that's actually a lovely answer! I'd accept it. <3 – OyaMist Jun 12 '18 at 13:31
  • @SDsolar question edited. Also included all created users. adminmiaou is no more sudoer but pi still is. – hello world Jun 12 '18 at 22:10
  • All good. I agree that backing up your SD card would be a very good idea before proceeding. Here's a good way to do it using Win32DiskImager: howtogeek.com/341944/… – SDsolar Jun 13 '18 at 2:22

The situation continued to deteriorate till I could no more ssh (connection refused). It appears that simply unplugging and replugging the raspi finally solved the issue. The files where restored to a state prior to inconsistencies and prior to my latest modifications of sshd_config, so authentication through allowgroups was back ! I guess the restart triggered fsck and it seems now quite sure that a simple reboot through ssh when it was still working would have do the trick, anyway I did not dare to do this.

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