NAME

       lbdb_dotlock - Lock mail spool files.

SYNOPSIS

       lbdb_dotlock [-t|-f|-u|-d] [-r retries] file

DESCRIPTION

       dotlock  implements  the  traditional mail spool file locking method: To lock file, a file
       named file.lock is created.

OPTIONS

       -t     Just try.  dotlock won't actually lock a file, but inform the invoking  process  if
              it's at all possible to lock file.

       -f     Force  the  lock.   If  another  process holds a lock on file longer than a certain
              amount of time, dotlock will break that lock by removing the lockfile.

       -u     Unlock.  dotlock will remove file.lock.

       -d     Delete.  dotlock will lock file, remove it if  it  has  length  0,  and  afterwards
              remove file.lock.

       -r retries
              This  command  line option tells dotlock to try locking retries times before giving
              up or (if invoked with the -f command line option) break a lock.  The default value
              is 5.  dotlock waits one second between successive locking attempts.

FILES

       file.lock
              The lock file dotlock generates.

SEE ALSO

       fcntl(2), flock(2), lockfile(1), lbdb-fetchaddr(1)

DIAGNOSTICS

       dotlock gives all diagnostics in its return values:

       0 - DL_EX_OK
              The program was successful.

       1 - DL_EX_ERROR
              An unspecified error such as bad command line parameters, lack of system memory and
              the like has occurred.

       3 - DL_EX_EXIST
              The user wants to lock a file which has been locked by another process already.  If
              dotlock  is  invoked  with  the -f command line option, dotlock won't generate this
              error, but break other processes' locks.

       4 - DL_EX_NEED_RPIVS
              This return value only occurs if dotlock has been invoked with the -t command  line
              option.   It  means that dotlock will have to use its group mail privileges to lock
              file.

       5 - DL_EX_IMPOSSIBLE
              This return value only occurs if dotlock has been invoked with the -t command  line
              option.  It means that dotlock is unable to lock file.

NOTES

       dotlock  tries  to  implement  an  NFS-safe  dotlocking  method  which  was  borrowed from
       lockfile(1).

       If the user can't open file for reading with his normal privileges,  dotlock  will  return
       the  DL_EX_ERROR exit value to avoid certain attacks against other users' spool files. The
       code carefully avoids race conditions when checking permissions; for details of  all  this
       see the comments in dotlock.c.

HISTORY

       dotlock is part of the Mutt mail user agent package.  It has been created to avoid running
       mutt with group mail privileges.

AUTHOR

       Thomas Roessler <roessler@guug.de>