lbdb_dotlock - Lock mail spool files.
lbdb_dotlock [-t|-f|-u|-d] [-r retries] file
dotlock implements the traditional mail spool file locking method: To lock file, a file named file.lock is created.
- Just try. dotlock won't actually lock a file, but inform the invoking process if it's at all possible to lock file.
- 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.
- Unlock. dotlock will remove file.lock.
- 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.
- The lock file dotlock generates.
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.
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.
dotlock is part of the Mutt mail user agent package. It has been created to avoid running mutt with group mail privileges.
Thomas Roessler <email@example.com>