I would like to see what’s happening in my app server folders, i.e. which files are changed by process x or which *.war files have been changed (replaced/created) in the last x minutes.
Is there a tool in Linux to help with this?
Answers:
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Method 1
Strace (as outlined above) is one way to check the actions of a specified running software.
Some command like watch find dir/ -mmin 1 may also help to check for changes of the past minute in some directory.
Depending on what exactly you’re looking for, inotify-tools is probably another tool of trade here.
For example, inotifywait -mr dir/ monitors changes in the given directory and instantly gives you feedback of any application trying to open/read/write/close a file. However, inotify doesn’t give you feedback on which application or process is accessing the file – that’s something strace does do.
Please do know system-level monitoring is usually of limited use for java software running in some application container environment, as you only do see the container (e.g. Tomcat), but not the actual application (e.g. .war)) interacting with the system.
Method 2
Depending on your exact needs, you might want to look into inotify and/or FAM/GAMIN solutions.
Method 3
You can get information about which files accessed by process by lsof:
lsof -n -p `pidof your_app`
And vice verse, you can get pid of process that write/read to some file:
lsof -n -t file
Method 4
You could use strace to monitor all system-calls of a process, which includes all file access.
When starting a program:
$ strace ./myserver
you can also attach strace to a running process via it’s PID:
$ ps aux | grep myserver me 1859 0.0 0.0 25288 424 ? Ss Sep02 0:00 myserver $ strace -p 1859
Method 5
watch find dir/ -mmin 1 did not work for me, what did was simply copy and diff:
cp -r dir /tmp/olddir # initialize/whatever diff -r dir /tmp/olddir
It’s quite resource-intensive, but it shows all changes between the snapshot and diff time.
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