bionic (1) lbdb_dotlock.1.gz

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>