Context:
I want to use log4j to write audit-related logs to a specific log file, let's say audit.log. I don't want to use syslogappender(udp based) because I don't want to be tolerant to data loss. Plus, I am using logrotate to rotate the audit.log when the file gets to certain size.
Problem:
I am encountering is that, when logrotate rotates the file audit.log to audit.log.1, log4j keeps writing to audit.log.1 other than writing to the audit.log.
Possible approaches:
I know I can use rollingfileappender to do the log rotation other than use logrotate, so when rollingfileappender rolls the file, it switch to the new file without hassles. But the reason I can't use rollingfileappender is that I want to use logrotate's post rotate feature to trigger some scripts after the rotation happens which can't be provided by rollingfileappender.
Another desperate way I can think of is to write a log4j customized appender myself to close the log file(audit.log.1) and open the new one(audit.log) when it detects the file is rotated.
I never used ExternallyRolledFileAppender, but if it's possible to use logrotate post rotate to send the signal to ExternallyRolledFileAppender and make log4j aware the file is rotated, and start writing to the new file?
Question:
Just wondering is there some appender like that already been invented/written? or do I have other options to solve this?
Check out logrotate's copytruncate option, it might help your case:
copytruncate
Truncate the original log file to zero size in place
after creating a copy, instead of moving the old log
file and optionally creating a new one. It can be
used when some program cannot be told to close its
logfile and thus might continue writing (appending) to
the previous log file forever. Note that there is a
very small time slice between copying the file and
truncating it, so some logging data might be lost.
When this option is used, the create option will have
no effect, as the old log file stays in place
Related
I have a logrotate configuration which is given below.
/var/log/Test.log {
size 50k
missingok
rotate 10
notifempty
create 0640 root root
}
The file is rotating successfully once it reached the size of 50kb in the below format
Test.log.1
Test.log.2
Test.log.3
What I can do if I want to rotate files in the below format
Test_1.log
Test_2.log
Test_3.log
Try this one,it should help you.
/var/log/Test.log {
...
postrotate
/usr/bin/mv Test.log.1 Test_1.log
...
endscript
}
OK, so the problem here is that logrotate uses these filename extensions to keep track of its rotations. So if you have x.log, it inherently needs a predictable, sequential extension to keep track of what is what; i.e. x.log.1 is the first rotation, x.log.2 is the second, etc.
By renaming the file like that, you're moving the extension to the middle of the file and subsequently leaving each file with the same extension: .log. So as far as logrotate is concerned, it will think those are all unrelated files, not rotations of a previous log.
E.g., if you rename Test.log.1 to Test_1.log, and leave that file in the same folder, logrotate won't know that it's a rotation of Test.log and create a new Test.log.1 upon next rotation. And so on, and so on.
So the short answer is no, there is no logrotate directive that will rename a file like you want. You will have to create this functionality yourself using a postrotate script, and you will also have to (at some point) move these files out of the var/log/ directory once they're renamed, using either said postrotate script or the olddir directive.
The dateext directive might also be useful, as in my opinion date extensions are typically more user-friendly than numerical ones.
say biz.log:
I read the logrotate(8) defaults to (1) rename the old log file with the date, biz.log.20220129 and then (2) create a new file with the origin name, and finally
(3) change the process's log output to the new file inode.
My question is the fact that the biz-process uses the inode instead of the file makes step1, and step2 reasonable. But how does the (3) work? I am not sure how logrotate can tell the process the log file should be reopened, and do I have to add some code to handle this in my project?
It requires cooperation between logrotate and application. Logrotate must be configured through postrotate scripts, to emit signal (i.e. SIGUSR), which application must handle - by reopening log files by their name. Actually one may also use different interprocess communication method, but i believe signals are common. See for example discussion on logrotate for httpd configuration (https://serverfault.com/questions/262868/logrotate-configuration-for-httpd-centos).
If there is no option to modify application, to work with signals for file rotation, one may configure logrotate to use copytruncate option - where logrotate copy current file to backup file, and then truncates current file to 0 bytes. If file is opened by application in append mode, it should be seamless. See https://man7.org/linux/man-pages/man8/logrotate.8.html copytruncate section.
I want empty a continuously printing log file in production,
I use below command:
echo > filename.log
I know the above command is used to empty continuously running log file if that file is getting too big.
But my query is - What happens to the old file?Does that file gets backed up or the previous data is lost forever?
How can I get the previous logs?
Previous data is basically lost forever.
You can search for backup files.There can be a file named filename.log~ for filename.log in the same directory.
It depends. If the other program has the log file permanently opened, the current log will be unlinked from its folder and your program just creates a brand new empty file. But the other program will still log to its now innaccessible file which will only be actually deleted when the program close it (or ends).
If the other program consistently uses the pattern open-write-close, you just erase previous content and new data will to that new file.
In any case old content is lost, but in first one the disk space is not reclaimed. If you want to keep it, you should google for log rotate
I am using file as input for logs in logstash . My log files are rotated daily so , I wanted to ask how can we configure file plugin of logstash so that it work with the files that are rotated daily. And adding to this, is log rotation available with file beat as well.
I am trying to answer your questions in part.
First - log rotation.
From the docs:
Note that the rotated filename will be treated as a new file so if
start_position is set to beginning the rotated file will be
reprocessed.
https://www.elastic.co/guide/en/logstash/current/plugins-inputs-file.html
That means, that if you have a rename in your file rotation, you will likely double your file (unless the path excludes the renamed file I believe).
If your path excludes your renamed file, then it should be fine.
I fixed this in a different way (in java and python accordingly).
I disable renaming of files and instead name the log file with the date prefix. So for me, in my java app, the file name is:
my-server-log-%h-%d.log
Since I am working in a distributed environment, I incorporate the hostname into my logfile name.
%h = hostname
%d = date
This ends up in my file being named:
my-server-log-pandaadb-2016-06-20.log
This file is never renamed. I modified my rotation algorithm to simply not rename and instead at midnight create a new file and leave the previous file untouched.
This has the effect that logstash (correctly) knows that it has read all lines in the previous file. It picks up the new file since I am using wildcards in my input. No logs are duplicated.
This also works quite well in combination with rsync by the way.
I hope that helps,
Artur
Edit: I have not worked with filebeat so far, so I can't comment on that part.
I using centos5.8
I wonder why syslog stop writing log after certain log edited.
for example, after cut the line of /var/log/messages, syslog doesn't write new log.
Just old logs are remained.
But If I delete the messages file and reboot the system, syslog works fine.
Is there any ways, syslogd write new logs continuosely after edit certain log??
It depends how exactly a file is edited.
Remember that syslogd keeps the file open for continuously writing. If your editor writes a new file with the old name after unlink()ing or rename()ing the old file, that old file remains in operation for syslogd. The new file, however, remains untouched.
It can be informed about the new file to be used with the HUP signal.
Well, that would depend on how syslogd works. I should mention that it's probably not a good idea to edit system log files, by the way :-)
You may have been caught out by one peculiarity of the way UNIX file systems can work.
If process A has a file open and is writing to it, process B can go and just delete the file (either with something like rm or, as seems likely here, in an edit session which deletes the old file and rewrites a new one).
Deletion of that original file does not destroy the data, it simply breaks the link between the file name (the directory entry) and that data.
A process that has the original file open can continue to write to it as long as it wants and, since there's no entry in the file system for it, you can't (easily) see it.
A new file with that file name may be bought into existence but process A will not be writing to it, it will be writing to the original. There will be no connection between the old and the new file.
You'll sometimes see this effect when you're running low on disk space and decide to delete a lot of files to clear it up somewhat. If processes have those files open, deleting them will not help you at all since the space is still being used (and quite possibly the usage is increasing).
You have to both delete the files and somehow convince those processes holding them open to relinquish them.
If you edited /var/log/syslog you need to restart the syslog service afterwards, because syslogd needs to open the file handle again.