Wednesday, May 13, 2009

Which Process Deleted My File ?

Ever asked this question before: "Which process deleted my file ?". In Solaris 10, you can rely on DTrace to help you to figure that out. A simple one-liner is all your need.

# dtrace -qn 'syscall::unlink:entry {printf("PID=%d, CMD=%s, FILE=%s\n", pid, curpsinfo->pr_psargs, copyinstr(arg0));}'
PID=26993, CMD=/usr/sbin/cron, FILE=/tmp/croutTKG5dKjU0
PID=26993, CMD=/usr/sbin/cron, FILE=/tmp/croutUKG6dKjU0
PID=13668, CMD=/usr/bin/mail chihung, FILE=/var/tmp/mail5iaGSA
PID=10389, CMD=/usr/sbin/cron, FILE=/tmp/croutLIEDWaOsu
PID=13669, CMD=/usr/lib/sendmail -oi -- chihung, FILE=./xfn4DCU0Ua013669
PID=26993, CMD=/usr/sbin/cron, FILE=/tmp/croutVKG7dKjU0
PID=13678, CMD=/usr/bin/mail chihung, FILE=/var/tmp/mailq0aWTA
PID=13679, CMD=/usr/lib/sendmail -oi -- chihung, FILE=./xfn4DCV0BF013679
PID=26993, CMD=/usr/sbin/cron, FILE=/tmp/croutWKG8dKjU0
PID=13689, CMD=/usr/bin/mail chihung, FILE=/var/tmp/mailtFaiVA
PID=13690, CMD=/usr/lib/sendmail -oi -- chihung, FILE=./xfn4DCW0qf013690

In UNIX, the system call to delete/remove file is "unlink" and you can see that the "path" of the file to be deleted is the only parameter passed to the function call and that's why we de-reference the pointer using copyinstr(arg0)

# man -s 2 unlink
System Calls                                            unlink(2)

     unlink, unlinkat - remove directory entry


     int unlink(const char *path);

     int unlinkat(int dirfd, const char *path, int flag);

     The unlink() function removes a link  to  a  file.  If  path
     names  a  symbolic  link, unlink() removes the symbolic link
     named by path and does not  affect  any  file  or  directory
     named by the contents of the symbolic link.
      Otherwise, unlink() removes the link named by the  pathname
     pointed to by path and decrements the link count of the file
     referenced by the link.

Wanna to learn that, here are some tutorial materal I gathered from the web:

You may also want to download the DTraceToolkit to see how powerful DTrace is.

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Blogger Raymond Tay said...

Nice illustration of the DTrace script

11:53 PM  

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