DOTLOCKFILE

NAME

dotlockfile - Utility to manage lockfiles

SYNOPSIS

/usr/bin/dotlockfile [-p] [-c] [-u] [-m] [-l|-u] [-r retries] [lockfile]

DESCRIPTION

Dotlockfile is a command line utility to safely create, test and remove lockfiles. Lockfiles are created in an NFS-safe way. Dotlockfile can lock and unlock mailboxes even if the mailspool directory is only writable by group mail.

The name dotlockfile comes from the way mailboxes are locked for updates on a lot of UNIX systems. A lockfile is created with the same filename as the mailbox but with the string ".lock" appended.

The names dotlock and lockfile were already taken - hence the name dotlockfile :).

OPTIONS

-l: Create a lockfile. This is the default.
-u: Remove a lockfile.
-c: Check for the existence of a valid lockfile.
-p: Write the process-id of the calling process into the lockfile. Also when testing for an existing lockfile, check the contents for a process-id to find out if the lockfile is still valid.
-r retries: The number of times dotlockfile tries to acquire the lock before giving up. The initial sleep after failing to acquire the lock is 5 seconds. After each next try, a sleep of 5 seconds extra occurs up to a maximum sleep of 60 seconds between tries.
-m: Lock or unlock the current users mailbox. The path to the mailbox is the default system mailspool directory (usually /var/mail) with the username as gotten from getpwuid() appended. If the environment variable $MAIL is set, that is used instead. Then the string ".lock" is appended to get the name of the actual lockfile.
lockfile: The lockfile to be created/removed, unless the -m option is in effect.

RETURN VALUE

Zero on success, and non-zero on failure. For the -c option, sucess means that a valid lockfile is already present. When locking (the default, or the -l option) dotlockfile returns the same values as the library function lockfile_create(3).

NOTES

The lockfile is created exactly as named on the command line. The extension .lock is not automatically added.

This utility is a lot like the lockfile(1) utility included with procmail, and the mutt_dotlock(1) utility included with mutt. However the command-line arguments differ, and so does the return status. It is believed that dotlockfile is the most flexible implementation, since it automatically detects when it needs to use priviliges to lock a mailbox, and does it safely.

BUGS

None known.

AUTHOR

Miquel van Smoorenburg, miquels@cistron.nl