dotlockfile
Utility to manage lockfiles
Synopsis
/usr/bin/dotlockfile
[-l [-r retries]
|-u|-t|-c]
[-p] [-m|lockfile]
add an example, a script, a trick and tips
examples
source
if (
/usr/bin/dotlockfile -l -r 0
/var/run/metacarta/reset-crawler-in-progress.lock ) ; then
trap "/usr/bin/dotlockfile -u
/var/run/metacarta/reset-crawler-in-progress.lock" EXIT
trap "/usr/bin/dotlockfile -u
/var/run/metacarta/reset-crawler-in-progress.lock" EXIT
# This will also block postgres-maintenance from
running
source
fi
lockfile=/var/lock/check_exim_mailq
dotlockfile -r 0 -p $lockfile
|| exit
mailq=$(find $spool_dir -iname
'*-H' | wc -l)
[ $mailq -ge
$critical ]
&& exit 2
[ $mailq -ge
$warning ]
&& exit 1
dotlockfile -u $lockfile
exit 0
description
dotlockfile
is a command line utility to reliably create, test and
remove lockfiles. It creates lockfiles reliably on
local and NFS filesystems, because the crucial steps of
testing for a preexisting lockfile and creating it are
performed atomically by a single call to
link(2). Manpage lockfile_create(3) describes
the used algorithm.
dotlockfile
is installed with attribute SETGID mail
and thus can also be used to 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 if no
preexisting valid lockfile is found, else wait and retry
according to option -r. This option is the
default.
A lockfile is
treated as valid,
• if it holds the process-id of
a running process,
• or if it does not hold any
process-id and has been touched less than
5 minutes ago (timestamp is younger than
5 minutes).
-r retries
The number of times
dotlockfile retries to acquire the lock if it failed
the first time before giving up. The initial sleep after
failing to acquire the lock is 5 seconds. After each
retry the sleep intervall is increased incrementally by
5 seconds up to a maximum sleep of 60 seconds
between tries. The default number of retries is 5. To try
only once, use "-r 0". To try
indefinitely, use "-r -1".
-u
Remove a lockfile.
-t
Touch an existing lockfile (update the timestamp).
Useful for lockfiles on NFS filesystems. For lockfiles on
local filesystems the -p option is
preferable.
-c
For debugging only: Check for the existence of a
valid lockfile.
Note: Testing
for a preexisting lockfile and writing of the lockfile
must be done by the same "dotlockfile
-l" or "dotlockfile
-m" command, else the lockfile creation
cannot be reliable.
-p
Write the
process-id of the calling process into the
lockfile. Also when testing for an existing lockfile, check
the contents for the process-id of a running
process to verify if the lockfile is still valid. Obviously
useful only for lockfiles on local filesystems.
-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 or
removed. Must not be specified, if the -m
option is in effect.
notes
The lockfile is created exactly as named on the command line. The
extension ".lock" is not automatically appended.
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.
The above mentioned lockfile_create(3) manpage is present
in the liblockfile-dev package.
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 with the -l option)
dotlockfile returns the same values as the library
function lockfile_create(3). Unlocking a non-existant
lockfile is not an error.
bugs
None known.
see also
lockfile_create,
maillock
author
Miquel van
Smoorenburg, miquels[:at:]cistron[:dot:]nl