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flock - Linux Command

       flock [-sxon] [-w timeout] lockfile [-c] command...

       flock [-sxun] [-w timeout] fd

       This  utility  manages  flock(2) locks from within shell scripts or the
       command line.

       The first form wraps the lock around the executing a command, in a man-
       ner similar to su(1) or newgrp(1).  It locks a specified file, which is
       created (assuming appropriate permissions),  if  it  does  not  already

       The  second  form  is  conveninent inside shell scripts, and is usually
       used the following manner:

         flock -s 200
         # ... commands executed under lock ...
       ) 200>/var/lock/mylockfile

       The mode used to open the file doesn’t matter to flock; using >  or  >>
       allows  the  lockfile  to be created if it does not already exist, how-
       ever, write permission is required; using  <  requires  that  the  file
       already exists but only read permission is required.

       By  default,  if  the  lock cannot be immediately acquired, flock waits
       until the lock is available.

       -s, --shared
              Obtain a shared lock, sometimes called a read lock.

       -x, -e, --exclusive
              Obtain an exclusive lock, sometimes called a write  lock.   This
              is the default.

       -u, --unlock
              Drop  a  lock.   This  is  usually not required, since a lock is
              automatically dropped when the file is closed.  However, it  may
              be  required  in special cases, for example if the enclosed com-
              mand group may have forked a background process which should not
              be holding the lock.

       -n, --nb, --nonblock
              Fail  (with an exit code of 1) rather than wait if the lock can-
              not be immediately acquired.

       -w, --wait, --timeout seconds
              Fail (with an exit code of 1) if the  lock  cannot  be  acquired
              within  seconds seconds.  Decimal fractional values are allowed.

       Copyright © 2003-2006 H. Peter Anvin.
       This is free software; see the source for copying conditions.  There is
       NO  warranty;  not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR


flock utility                     4 Feb 2006                          FLOCK(1)

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