Final test: Inside the system: resources, kernel, processes

Read the output

Which process holds the queue lock?

$ sudo lsof /var/lib/mailer/queue.lock
COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME
qclean  1015 root    3wW  REG  253,4        0 308090 /var/lib/mailer/queue.lock
mailer  1022 root    4w   REG  253,4        0 308090 /var/lib/mailer/queue.lock

• A qclean — it has W in the FD column.
• B mailer — it has the file open for writing.
• C Both in turns: lsof shows them together.