Sunday, June 7, 2009

Strace

When you have a problem with your web server it is often quite useful to use a system call tracer to see what the web server is doing.
strace

The strace command would be :-

strace -fe verbose=all -e write=all -o /tmp/strace.log -p [pid]

-f traces all child processes as they are created byt he currently traced process as a result of the fork() system call.

-e is a qualifying expression which modifies which events to trace or how to race them

verbose=all dereferences structures for all system calls

write=all performs a full hexadecimal and ASCII dump of all the data written to all file descriptors

-o output file

-p process id to trace

Replace -p [pid] with [command] to trace a specific command.

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