Mailman stale lock files keep the service from starting properly

Symptoms

If you are getting the following errors when trying to restart Mailman with the /scripts/restartsrv_mailman command, you may have stale lock files on the system:

[root@server ~]# /scripts/restartsrv_mailman 
Waiting for “mailman” to start ……warn [restartsrv_mailman] The system encountered an error while starting the “mailman” service with the command “/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl -s start”: The subprocess reported error number 1 when it ended.
…warn [restartsrv_mailman] The system encountered an error while starting the “mailman” service with the command “/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl -s start”: The subprocess reported error number 1 when it ended.
…failed.

Cpanel::Exception::Services::StartError
Service Status

Service Error
 (XID mtkuud) The “mailman” service failed to start.

Startup Log
 Traceback (most recent call last):
   File "/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl", line 556, in <module>
     main()
   File "/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl", line 391, in main
     lock = acquire_lock(force)
   File "/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl", line 215, in acquire_lock
     lock = acquire_lock_1(force)
   File "/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl", line 203, in acquire_lock_1
     if not force or qrunner_state():
   File "/usr/local/cpanel/3rdparty/mailman/bin/mailmanctl", line 187, in qrunner_state
     os.kill(pid, 0)
 OSError: [Errno 1] Operation not permitted

mailman has failed. Contact your system administrator if the service does not automagically recover.

Workaround

While it's hard to say for sure what may have caused the issue, you can move those files out of the way to get Mailman working again by running the following commands:

mkdir /root/mailmam_lockfiles

mv /usr/local/cpanel/3rdparty/mailman/locks/* /root/mailmam_lockfiles

/scripts/restartsrv_mailman