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system call

Applications that perform a lot of memory accesses (several GBs) may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses. HugeTLBfs is memory management feature offered in Linux kernel, which is valuable for applications that use a large virtual address space. It is especially useful for database applications such as MySQL, Oracle and others. Other server software that uses the prefork or similar (e.g. Apache web server) model will also benefit.

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strace is a useful diagnostic, instructional, and debugging tool. It can save lots of headache. System administrators, diagnosticians and trouble-shooters will find it invaluable for solving problems with programs for which the source is not readily available since they do not need to be recompiled in order to trace them. This is also useful to submit bug reports to open source developers.

Each line in the trace contains the system call name, followed by its arguments in parentheses and its return value.

Run strace against /bin/foo and capture its output to a text file in output.txt:
$ strace -o output.txt /bin/foo
You can strace the webserver process and see what it's doing. For example, strace php5 fastcgi process, enter:
$ strace -p 22254 -s 80 -o /tmp/debug.lighttpd.txt
To see only a trace of the open, read system calls, enter :
$ strace -e trace=open,read -p 22254 -s 80 -o debug.webserver.txt
Where,

  • -o filename : Write the trace output to the file filename rather than to screen (stderr).
  • -p PID : Attach to the process with the process ID pid and begin tracing. The trace may be terminated at any time by a keyboard interrupt signal (hit CTRL-C). strace will respond by detaching itself from the traced process(es) leaving it (them) to continue running. Multiple -p options can be used to attach to up to 32 processes in addition to command (which is optional if at least one -p option is given).
  • -s SIZE : Specify the maximum string size to print (the default is 32).

Refer to strace man page for more information:
$ man strace