Monitoring file locks, locked using flock

Question

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?

Answer 1

• 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

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• 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
  

Answer 2

fuser /tmp/file will list all processes which have the file open, including those that have a lock on it.