Log-Rotate

On Linux, there is the logrotate command, which will very nicely take a text file and, based on parameters, “rotate” the file. This is, obviously, very nice for breaking up log files into workable chunks and retaining some backlog of these logs for a set amount of time. Unfortunately, this sort of thing doesn’t exist natively for Windows.

Fortunately, someone made a powershell module that just… does this. Like, literally, just does this but in Windows. However, the documentation is kind of confusing because it kind of works like a powershell commandlet, but then relies on the documentation of the Linux command above, which is kind of confusing. So, let me throw down here what I’ve done to try and fill in some gaps for those of us having some trouble jumping that gap.

First thing’s first, you’ll need to install the module. Once done, you’ll be able to run log-rotate -config <Config File Location> -state <State File Location>. The config file location and state file location will point to a config and state file, which I’ve personally named logrotate.conf and logrotate.status. This is the only thing we need in Powershell.

Now the magic sauce: the config file. I’m going to put an example below, then we can talk some more about what’s going on in here.

# Defaults 
daily
size 100M
missingok
rotate 7
create
extension .txt
ifempty
olddir .\Log Archive

# Specific Settings
C:\Logs\Job1Log.txt {
}

C:\Job2Logs\*.txt {
extension .log
monthly
}

C:\Job3Logs {
size 500M
}

The top section is settings that will be applied to all of the log files you are trying to rotate. Below that, you’ll see sections for whch individual files, folders, and wildcard-defined files and folders log-rotate will interact with when run. Log-rotate doesn’t run in the directory you’re running you shell in, it’ll run against these configured directories. Within those brackets, further settings can be set that will override the “defaults” set above. You can check the logrotate page for explanations and definitions of what these settings do, but I’ll call out a few things that needed some further explaining from the documentation.

• olddir doesn’t need quotation marks for folders with spaces. It will use a relative path, so in the first case, C:\Logs\Job1Log.txt will be rotated to C:\Logs\Log Archive\Job1log.1.txt.
• extension needs the period before the extension. Note here that I’ve defined this in the “defaults” section as .txt. Remember that every time log-rotate runs, it will check for files that match, and then rotate them to include .txt at the end. This is useful to make it easier to open rotated files with your default reader, but remember that log.txt will be rotated to log.txt and log.1.txt, which means the next time log-rotate runs, both log.txt and log.1.txt will get rotated, resulting in log.txt, log.1.txt, and log.1.1.txt which is not desired. I’ve specified an olddir folder to move older files into to help avoid this issue.

Finally, the state file can be basically left alone unless you need to reset things. It is just used to keep track of the state of your log files so that the next time log-rotate is run, it’ll know how old the files are, for example.