1LOCKFILE(1) General Commands Manual LOCKFILE(1)
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6 lockfile - conditional semaphore-file creator
7
9 lockfile -sleeptime | -r retries |
10 -l locktimeout | -s suspend | -! | -ml | -mu | filename ...
11
13 lockfile can be used to create one or more semaphore files. If lock‐
14 file can't create all the specified files (in the specified order), it
15 waits sleeptime (defaults to 8) seconds and retries the last file that
16 didn't succeed. You can specify the number of retries to do until
17 failure is returned. If the number of retries is -1 (default, i.e.,
18 -r-1) lockfile will retry forever.
19 If the number of retries expires before all files have been created,
21 lockfile returns failure and removes all the files it created up till
22 that point.
23 Using lockfile as the condition of a loop in a shell script can be done
25 easily by using the -! flag to invert the exit status. To prevent in‐
26 finite loops, failures for any reason other than the lockfile already
27 existing are not inverted to success but rather are still returned as
28 failures.
29 All flags can be specified anywhere on the command line, they will be
31 processed when encountered. The command line is simply parsed from
32 left to right.
33 All files created by lockfile will be read-only, and therefore will
35 have to be removed with rm -f.
36 If you specify a locktimeout then a lockfile will be removed by force
38 after locktimeout seconds have passed since the lockfile was last modi‐
39 fied/created (most likely by some other program that unexpectedly died
40 a long time ago, and hence could not clean up any leftover lockfiles).
41 Lockfile is clock skew immune. After a lockfile has been removed by
42 force, a suspension of suspend seconds (defaults to 16) is taken into
43 account, in order to prevent the inadvertent immediate removal of any
44 newly created lockfile by another program (compare SUSPEND in proc‐
45 mail(1)).
46 Mailbox locks
48 If the permissions on the system mail spool directory allow it, or if
49 lockfile is suitably setgid, it will be able to lock and unlock your
50 system mailbox by using the options -ml and -mu respectively.
51
53 Suppose you want to make sure that access to the file "important" is
54 serialised, i.e., no more than one program or shell script should be
55 allowed to access it. For simplicity's sake, let's suppose that it is
56 a shell script. In this case you could solve it like this:
57 ...
58 lockfile important.lock
59 ...
60 access_"important"_to_your_hearts_content
61 ...
62 rm -f important.lock
63 ...
64 Now if all the scripts that access "important" follow this guideline,
65 you will be assured that at most one script will be executing between
66 the `lockfile' and the `rm' commands.
67
69 LOGNAME used as a hint to determine the invoker's login‐
70 name
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73 /etc/passwd to verify and/or correct the invoker's loginname
74 (and to find out his HOME directory, if needed)
75 /var/spool/mail/$LOGNAME.lock
77 lockfile for the system mailbox, the environment
78 variables present in here will not be taken from
79 the environment, but will be determined by look‐
80 ing in /etc/passwd
81
83 rm(1), mail(1), sendmail(8), procmail(1)
84
86 Filename too long, ... Use shorter filenames.
87 Forced unlock denied on "x"
89 No write permission in the directory where lock‐
90 file "x" resides, or more than one lockfile try‐
91 ing to force a lock at exactly the same time.
92 Forcing lock on "x" Lockfile "x" is going to be removed by force be‐
94 cause of a timeout (compare LOCKTIMEOUT in proc‐
95 mail(1)).
96 Out of memory, ... The system is out of swap space.
98 Signal received, ... Lockfile will remove anything it created till
100 now and terminate.
101 Sorry, ... The retries limit has been reached.
103 Truncating "x" and retrying lock
105 "x" does not seem to be a valid filename.
106 Try praying, ... Missing subdirectories or insufficient privi‐
108 leges.
109
111 Definitely less than one.
112
114 The behavior of the -! flag, while useful, is not necessarily intu‐
115 itive or consistent. When testing lockfile's return value, shell
116 script writers should consider carefully whether they want to use the
117 -! flag, simply reverse the test, or do a switch on the exact exit‐
118 code. In general, the -! flag should only be used when lockfile is
119 the conditional of a loop.
120
122 Lockfile is NFS-resistant and eight-bit clean.
123
125 Calling up lockfile with the -h or -? options will cause it to display
126 a command-line help page. Calling it up with the -v option will cause
127 it to display its version information.
128 Multiple -! flags will toggle the return status.
130 Since flags can occur anywhere on the command line, any filename start‐
132 ing with a '-' has to be preceded by './'.
133 The number of retries will not be reset when any following file is be‐
135 ing created (i.e., they are simply used up). It can, however, be reset
136 by specifying -rnewretries after every file on the command line.
137 Although files with any name can be used as lockfiles, it is common
139 practice to use the extension `.lock' to lock mailfolders (it is ap‐
140 pended to the mailfolder name). In case one does not want to have to
141 worry about too long filenames and does not have to conform to any oth‐
142 er lockfilename convention, then an excellent way to generate a lock‐
143 filename corresponding to some already existing file is by taking the
144 prefix `lock.' and appending the i-node number of the file which is to
145 be locked.
146
148 This program is part of the procmail mail-processing-package (v3.24)
149 available at http://www.procmail.org/ or ftp.procmail.org in pub/proc‐
150 mail/.
151
153 There exists a mailinglist for questions relating to any program in the
154 procmail package:
155 <procmail-users@procmail.org>
156 for submitting questions/answers.
157 <procmail-users-request@procmail.org>
158 for subscription requests.
159 If you would like to stay informed about new versions and official
161 patches send a subscription request to
162 procmail-announce-request@procmail.org
163 (this is a readonly list).
164
166 Stephen R. van den Berg
167 <srb@cuci.nl>
168 BuGless LOCKFILE(1)