multilog — reads a sequence of lines from stdin and appends selected lines to any number of logs.
script consists of any number of arguments.
Each argument specifies one action.
The actions are carried out in order for each line of input.
Note that actions may contain shell metacharacters that need to be quoted when multilog is run from a shell.
multilog exits 0 when it sees the end of stdin. If stdin has a partial final line then multilog inserts a final newline.
multilog writes a message to stderr and exits 111, without reading any input, if it runs out of memory or if another multilog process is writing to one of the same automatically rotated logs.
If multilog has trouble writing to disk after it starts reading input, it writes a message to stderr, pauses, and tries again, without losing any data. Note that this may block any program feeding input to multilog.
If multilog receives a TERM signal, it will read and process data until the next newline, and then exit, leaving stdin at the first byte of data it has not processed.
Each line is initially selected. The action
deselects the line if
pattern matches the line.
selects the line if
pattern matches the line.
pattern is a string of stars and non-stars.
It matches any concatenation of strings matched by all the stars and non-stars in the same order.
A non-star matches itself.
A star before the end of
pattern matches any string that does not include the next character in
A star at the end of
pattern matches any string.
For example, the action
It does not select
-named[*]: Cleaned cache *
named: Cleaned cache of 3121 RRs.
The first star matches any string that does not include a right bracket.
deselects every line.
To save memory, multilog actually checks pattern against only the first 1000 characters of each line.
replaces the contents of
file with (the first 1000 bytes of) each selected line, padded with newlines to 1001 bytes.
There is no protection of
file against power outages.
For example, the sequence of actions -* +STAT* =log/status maintains
log/status as a copy of the most recent line starting with
@, a precise timestamp, and a space in front of each line, using the same format as tai64n(1).
This is required to be the first action.
Patterns apply to the line after the timestamp is inserted. For example, if
multilog t '-*' '+* fatal: *' ./main
reads the line
fatal: out of memory
then it will log a line such as
@400000003b4a39c23294b13c fatal: out of memory
with the first * matching the timestamp.
You can use tai64nlocal(1) to convert these timestamps to human-readable form.
dir starts with a dot or slash then the action
appends each selected line to a log named
dir does not exist, multilog creates it.
Do not attempt to write to one log from two simultaneous multilog processes, or two actions in one process.
The log format is as follows.
is a directory containing some number of old log files, a log file named
current, and other files for multilog to keep track of its actions.
Each old log file has a name beginning with
@, continuing with a precise timestamp showing when the file was finished, and ending with one of the following codes:
This file is completely processed and safely written to disk.
This file was being created at the moment of an outage. It may have been truncated and has not been processed.
Beware that NFS, async filesystems, and softupdates filesystems may discard files that were not safely written to disk before an outage.
While multilog is running,
current has mode 644.
If multilog sees the end of stdin, it writes
current safely to disk, and sets the mode of
current to 744.
When it restarts, it sets the mode of
current back to 644 and continues writing new lines.
When multilog decides that
current is big enough, it writes
current safely to disk, sets the mode of
current to 744, and renames
current as an old log file.
sets the maximum file size for subsequent
multilog will decide that
current is big enough if
(multilog will also decide that
current is big enough if it sees a newline within 2000 bytes of the maximum file size; it tries to finish log files at line boundaries.)
size must be between 4096 and 16777215.
The default maximum file size is 99999.
In versions 0.75 and above: If multilog receives an ALRM signal, it immediately decides that
current is big enough, if
current is nonempty.
sets the number of log files for subsequent
current, if multilog sees
num or more old log files, it removes the old log file with the smallest timestamp.
num must be at least 2.
The default number of log files is 10.
processor for subsequent
multilog will feed
processor and save the output as an old log file instead of
multilog will also save any output that
processor writes to descriptor 5, and make that output readable on descriptor 4 when it runs
processor on the next log file.
processor must exit nonzero if it has any trouble creating its output; multilog will then run it again.
Note that running
processor may block any program feeding input to multilog.
multilog was originally part of Daniel J. Bernstein's daemontools toolset in 2001. It replaced an earler Bernstein program named cyclog.