Lustre 1.6 Operations Manual

23.3 Troubleshooting with strace
The operating system makes strace (program trace utility) available. Use strace
to trace program execution. The strace utility pauses programs made by a process
and records the system call, arguments, and return values. This is a very useful tool,
especially when you try to troubleshoot a failed system call.
To invoke strace on a program:
$ strace
Sometimes, a system call may fork child processes. In this situation, use the -f
option of strace to trace the child processes:
$ strace -f
To redirect the strace output to a file (to review at a later time):
$ strace -o
Use the -ff option, along with -o, to save the trace output in filename.pid,
where pid is the process ID of the process being traced. Use the -ttt option to
timestamp all lines in the strace output, so they can be correlated to operations in
the lustre kernel debug log.
If the debugging is done in UML, save the traces on the host machine. In this
example, hostfs is mounted on /r:
$ strace -o /r/tmp/vi.strace
23-12 Lustre 1.6 Operations Manual • September 2008