(...)

Is this issue specific to ssh?  What happens if you locally (on SERVER)
try to su -l checkuser with UID=1001? Or use ftp or telnet?

Yes, it's specific to SSH authentication with keys. Password logins work fine.
I can su:

thecus:/var/log# su -l checkuser
[EMAIL PROTECTED]:~$
[EMAIL PROTECTED]:~$ su
Password:
thecus:/home/checkuser#

I can login via telnet (using a password).


Also, try turning up the debug in the sshd process to try and see more
of what is happening:

# For sshd_config
LogLevel DEBUG3

We need to see what happens between the last two lines and the above
might help:
sshd[18730]: debug1: temporarily_use_uid: 1001/1001 (e=0/0)
sshd[18730]: debug1: trying public key file /home/checkuser/.ssh/
authorized_keys
sshd[18730]: debug1: restore_uid: 0/0

There is something strange with the key:

Sep 8 11:27:23 thecus sshd[23596]: Failed none for checkuser from 192.168.111.181 port 35531 ssh2
Sep  8 11:27:23 thecus sshd[23596]: debug3: mm_request_receive entering
Sep 8 11:27:23 thecus sshd[23596]: debug3: monitor_read: checking request 20
Sep  8 11:27:23 thecus sshd[23596]: debug3: mm_answer_keyallowed entering
Sep 8 11:27:23 thecus sshd[23596]: debug3: mm_answer_keyallowed: key_from_blob: 0x69b00 Sep 8 11:27:23 thecus sshd[23596]: debug1: temporarily_use_uid: 1001/1001 (e=0/0) Sep 8 11:27:23 thecus sshd[23596]: debug1: trying public key file /home/checkuser/.ssh/authorized_keys
Sep  8 11:27:23 thecus sshd[23596]: debug1: restore_uid: 0/0
Sep 8 11:27:23 thecus sshd[23596]: debug1: temporarily_use_uid: 1001/1001 (e=0/0) Sep 8 11:27:23 thecus sshd[23596]: debug1: trying public key file /home/checkuser/.ssh/authorized_keys2
Sep  8 11:27:23 thecus sshd[23596]: debug1: restore_uid: 0/0
Sep 8 11:27:23 thecus sshd[23596]: debug3: mm_answer_keyallowed: key 0x69b00 is disallowed Sep 8 11:27:23 thecus sshd[23596]: debug3: mm_request_send entering: type 21
Sep  8 11:27:23 thecus sshd[23596]: debug3: mm_request_receive entering


So, why the key is allowed if UID=0, and is disallowed if UID!=0?


Last option: you initially said that there were no options enabled in
sshd_config to deny users - what about the group options DenyGroups and
AllowGroups?

There's no option which allows/denies groups in my config.

I even used the same sshd_config file from another server, to which I can login using the same key (where "checkuser" has UID=1001), but still, I could only login if "checkuser" had UID=0.


--
Tomasz Chmielewski
http://wpkg.org

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