Monday, December 15, 2014

Debugging calls to cifs.upcall

/usr/sbin/cifs.upcall is the request-key help program used to obtain certain data like kerberos keys or results of dns calls from userland processes.

It is sometimes necessary to debug the execution of this helper function for which I use the following methods.

1) Capture debug messages from cifs.upcall.

Edit /etc/rsyslog.conf and add the line

*.* /var/log/debug

Restart rsyslog service and confirm that the log file /var/log/debug has been created which will log all messages.

Attempt the call which will usually be the call to mount the cifs share. You should see the debug messages from cifs.upcall in /var/log/debug.

2) Strace cifs.upcall calls.

First move the original cifs.upcall file
# cd /usr/sbin; mv cifs.upcall cifs.upcall.orig

Create a new text file cifs.upcall with the following content.


echo $@ >> /tmp/upcall.log
strace -fxvto /tmp/ -s1000  /usr/sbin/cifs.upcall.orig $@

Make sure this is an executable
# chmod +x cifs.upcall

Now attempt the mount process. You will see the strace output in /tmp/

Howto: CIFS kerberos mount

Steps 1) I use a windows server is available with an AD configured. A samba server with kerberos configured can be used too. 2) Setup /e...