Skip to content

Useful commands

Kill unresponsive process

An unresponsive processe/service ignores the kill command. In order to shut down the process immediately use

kill -9 PID

where PID is the process ID.

This is equivalent to

kill -SIGKILL PID

The kill -SIGKILL command bypasses the standard shutdown routine and unsaved data will be lost.

Note

kill sends the SIGTERM signal by default, which allows the process to terminate gracefully.

find <DIR> -xtype l -delete

Sycalls ID to name mapping

The following command shows the mapping of syscall IDs to their names:

ausyscall --dump
Installation

ausyscall is part of the audit package.

sudo apt install auditd

Tracing system calls

strace allows to trace system calls and signals made by a process.

By default strace does not follow child processes, therefore the -f is often useful.

strace -f -o <STRACE_OUTPUT_FILE> <COMMAND>

-e can be used to filter the traced syscalls: -e trace=process traces only process-related syscalls.

strace -f -e trace=process -s 1024 -o <STRACE_OUTPUT_FILE> <COMMAND>

The -s option sets the maximum string size, which by default is relatively small.

Tip

strace-process-tree allows to visualize the strace -f output as a process tree.

strace-process-tree output 
$ strace-process-tree /tmp/trace.out
25510 make binary-package
  ├─25511 /bin/sh -c 'dpkg-parsechangelog | awk '\''$1 == "Source:" { print $2 }'\'''
  │   ├─25512 dpkg-parsechangelog
  │   │   └─25514 tail -n 40 debian/changelog
  │   └─25513 awk '$1 == "Source:" { print $2 }'
  ├─25515 /bin/sh -c 'dpkg-parsechangelog | awk '\''$1 == "Version:" { print $2 }'\'''
  │   ├─25516 dpkg-parsechangelog
  │   │   └─25518 tail -n 40 debian/changelog
  │   └─25517 awk '$1 == "Version:" { print $2 }'
  ├─25519 /bin/sh -c 'dpkg-parsechangelog | grep ^Date: | cut -d: -f 2- | date --date="$(cat)" +%Y-%m-%d'
  │   ├─25520 dpkg-parsechangelog
  │   │   └─25525 tail -n 40 debian/changelog
  │   ├─25521 grep ^Date:
  │   ├─25522 cut -d: -f 2-
  │   └─25523 date --date=" Thu, 18 Jan 2018 23:39:51 +0200" +%Y-%m-%d
  │       └─25524 cat
  └─25526 /bin/sh -c 'dpkg-parsechangelog | awk '\''$1 == "Distribution:" { print $2 }'\'''
      ├─25527 dpkg-parsechangelog
      │   └─25529 tail -n 40 debian/changelog
      └─25528 awk '$1 == "Distribution:" { print $2 }'

git-like patches

The diff command can be used to create git-like patches between two files or directories:

diff -uNr <OLD> <NEW> > changes.patch

This can be useful to generate patches for Spack.