DOTLOCKFILE
Section: Cistron Utilities (1)
Updated: Januari 5, 2017
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NAME
dotlockfile - Utility to manage lockfiles
SYNOPSIS
dotlockfile
-l
[
-r
retries]
[
-p]
<
-m |
lockfile>
dotlockfile
-l
[
-r
retries]
[
-p]
lockfile
cmd args...
dotlockfile
-u
| -t
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, so it can be left off.
A lockfile is treated as valid,
[bu] if it holds the
process-id
of a running process,
[bu] 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.
- -p
-
Write the
process-id
of the calling process (or dotlockfile itself if a command is executed)
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 given.
- command
-
Create lockfile, run the
command
, wait for it to exit, and remove lockfile.
RETURN VALUE
Zero on success, and non-zero on failure.
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.
If a command is executed, the return value does not correspond with that
of the command that was run. If the locking and unlocking was succesful,
the exit status is always zero.
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.
BUGS
None known.
SEE ALSO
lockfile_create(3),
maillock(3)
AUTHOR
Miquel van Smoorenburg,
miquels@cistron.nl
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- RETURN VALUE
-
- NOTES
-
- BUGS
-
- SEE ALSO
-
- AUTHOR
-
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