Provided by: procmail_3.22-19_i386 bug

NAME

       lockfile - conditional semaphore-file creator

SYNOPSIS

       lockfile -sleeptime | -r retries |
            -l locktimeout | -s suspend | -!  | -ml | -mu | filename ...

DESCRIPTION

       lockfile  can  be  used  to  create  one  or  more semaphore files.  If
       lockfile can't create all the specified files (in the specified order),
       it  waits  sleeptime  (defaults to 8) seconds and retries the last file
       that didn't succeed.  You can specify the number of retries to do until
       failure  is  returned.   If the number of retries is -1 (default, i.e.,
       -r-1) lockfile will retry forever.

       If the number of retries expires before all files  have  been  created,
       lockfile  returns  failure and removes all the files it created up till
       that point.

       Using lockfile as the condition of a loop in a shell script can be done
       easily  by  using  the  -!  flag to invert the exit status.  To prevent
       infinite loops, failures for any reason other than the lockfile already
       existing  are  not inverted to success but rather are still returned as
       failures.

       All flags can be specified anywhere on the command line, they  will  be
       processed  when  encountered.   The  command line is simply parsed from
       left to right.

       All files created by lockfile will be  read-only,  and  therefore  will
       have to be removed with rm -f.

       If  you  specify a locktimeout then a lockfile will be removed by force
       after locktimeout seconds have  passed  since  the  lockfile  was  last
       modified/created  (most  likely by some other program that unexpectedly
       died a long time ago,  and  hence  could  not  clean  up  any  leftover
       lockfiles).   Lockfile is clock skew immune.  After a lockfile has been
       removed by force, a suspension of suspend seconds (defaults to  16)  is
       taken  into  account,  in  order  to  prevent the inadvertent immediate
       removal of any newly  created  lockfile  by  another  program  (compare
       SUSPEND in procmail(1)).

   Mailbox locks
       If  the  permissions on the system mail spool directory allow it, or if
       lockfile is suitably setgid, it will be able to lock  and  unlock  your
       system mailbox by using the options -ml and -mu respectively.

EXAMPLES

       Suppose  you  want  to make sure that access to the file "important" is
       serialised, i.e., no more than one program or shell  script  should  be
       allowed  to access it.  For simplicity's sake, let's suppose that it is
       a shell script.  In this case you could solve it like this:
              ...
              lockfile important.lock
              ...
              access_"important"_to_your_hearts_content
              ...
              rm -f important.lock
              ...
       Now if all the scripts that access "important" follow  this  guideline,
       you  will  be assured that at most one script will be executing between
       the `lockfile' and the `rm' commands.

ENVIRONMENT

       LOGNAME                used  as  a  hint  to  determine  the  invoker's
                              loginname

FILES

       /etc/passwd            to verify and/or correct the invoker's loginname
                              (and to find out his HOME directory, if needed)

       /var/mail/$LOGNAME.lock
                              lockfile for the system mailbox, the environment
                              variables present in here will not be taken from
                              the  environment,  but  will  be  determined  by
                              looking in /etc/passwd

SEE ALSO

       rm(1), mail(1), sendmail(8), procmail(1)

DIAGNOSTICS

       Filename too long, ... Use shorter filenames.

       Forced unlock denied on "x"
                              No  write  permission  in  the  directory  where
                              lockfile "x" resides, or more than one  lockfile
                              trying to force a lock at exactly the same time.

       Forcing lock on "x"    Lockfile  "x"  is  going  to be removed by force
                              because of a  timeout  (compare  LOCKTIMEOUT  in
                              procmail(1)).

       Out of memory, ...     The system is out of swap space.

       Signal received, ...   Lockfile  will  remove  anything it created till
                              now and terminate.

       Sorry, ...             The retries limit has been reached.

       Truncating "x" and retrying lock
                              "x" does not seem to be a valid filename.

       Try praying, ...       Missing    subdirectories    or     insufficient
                              privileges.

BUGS

       Definitely less than one.

WARNINGS

       The  behavior  of  the  -!   flag,  while  useful,  is  not necessarily
       intuitive or consistent.  When testing lockfile's return  value,  shell
       script  writers  should consider carefully whether they want to use the
       -!  flag, simply reverse  the  test,  or  do  a  switch  on  the  exact
       exitcode.   In  general, the -!  flag should only be used when lockfile
       is the conditional of a loop.

MISCELLANEOUS

       Lockfile is NFS-resistant and eight-bit clean.

NOTES

       Calling up lockfile with the -h or -? options will cause it to  display
       a  command-line help page.  Calling it up with the -v option will cause
       it to display its version information.

       Multiple -!  flags will toggle the return status.

       Since flags can occur  anywhere  on  the  command  line,  any  filename
       starting with a '-' has to be preceded by './'.

       The  number  of  retries  will  not be reset when any following file is
       being created (i.e., they are simply used up).   It  can,  however,  be
       reset by specifying -rnewretries after every file on the command line.

       Although  files  with  any  name can be used as lockfiles, it is common
       practice to use the  extension  `.lock'  to  lock  mailfolders  (it  is
       appended to the mailfolder name).  In case one does not want to have to
       worry about too long filenames and does not  have  to  conform  to  any
       other  lockfilename  convention,  then  an  excellent way to generate a
       lockfilename corresponding to some already existing file is  by  taking
       the prefix `lock.' and appending the i-node number of the file which is
       to be locked.

SOURCE

       This program is part of the  procmail  mail-processing-package  (v3.22)
       available    at   http://www.procmail.org/   or   ftp.procmail.org   in
       pub/procmail/.

MAILINGLIST

       There exists a mailinglist for questions relating to any program in the
       procmail package:
              <procmail-users@procmail.org>
                     for submitting questions/answers.
              <procmail-users-request@procmail.org>
                     for subscription requests.

       If  you  would  like  to  stay informed about new versions and official
       patches send a subscription request to
              procmail-announce-request@procmail.org
       (this is a readonly list).

AUTHORS

       Stephen R. van den Berg
              <srb@cuci.nl>
       Philip A. Guenther
              <guenther@sendmail.com>