Monitoring file locks, locked using flock

filesinotifylock

I would like to get a list of pid's which hold shared lock on /tmp/file. Is this possible using simple command line tools?

Best Answer

  • From man lsof:

    FD is the File Descriptor number of the file or: FD is followed by one of these characters, describing the mode under which the file is open: 

              The mode character is followed by one of these lock characters, describing the type of lock applied to the file:

               R for a read lock on the entire file;
               W for a write lock on the entire file;
               space if there is no lock.

So R in 3uR mean that read/shared lock is issued by 613 PID.

#lsof /tmp/file
COMMAND PID    USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME
perl    613 turkish    3uR  REG    8,2        0 1306357 /tmp/file

  • Reading directly from /proc/locks is faster than lsof,

    perl -F'[:\s]+' -wlanE'
  BEGIN { $inode = (stat(pop))[1]; @ARGV = "/proc/locks" }
  say "pid:$F[4] [$_]" if $F[7] == $inode
' /tmp/file
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