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Linux Terminal Tricks

Auto Clean-up Package Configuration Conflicts Problems

In case there are error messages (when executing apt update) related to:

W: Target Packages (stable/binary-ppc64el/Packages) is configured multiple times in /etc/apt/sources.list:55 and /etc/apt/sources.list.d/docker.list:1
W: Target Packages (stable/binary-all/Packages) is configured multiple times in /etc/apt/sources.list:55 and /etc/apt/sources.list.d/docker.list:1
W: Target Translations (stable/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list:55 and /etc/apt/sources.list.d/docker.list:1

There's an automatic tool which can be use to clean up those configurations:

  • Install the prerequisites: sudo apt install python3-apt
  • Download the PYZ bundle (aptsources-cleanup.pyz) from the latest release.
  • Mark the PYZ bundle as executable: chmod a+x aptsources-cleanup.pyz
  • Run sudo ./aptsources-cleanup.pyz
  • Check sudo apt update again to see if the error messages disappear!

Check The Location of apt Installed Libraries/Packages

dpkg -L <package_name>

Or:

apt-file list <package_name>

Install a Package from .deb File

sudo dpkg -i package_file.deb

Remove an Installed Package Completely

$ sudo apt remove package_name
$ sudo apt purge package_name # remove files and configs
$ sudo apt autoclean          # remove old downloaded archive files

Clear Cache

  • To free pagecache:
# echo 1 > /proc/sys/vm/drop_caches
  • To free dentries and inodes:
# echo 2 > /proc/sys/vm/drop_caches
  • To free pagecache, dentries and inodes:
# echo 3 > /proc/sys/vm/drop_caches

Run the above three commands as root, or you can run a series of commands as below:

sudo sh -c 'echo 1 >/proc/sys/vm/drop_caches'
sudo sh -c 'echo 2 >/proc/sys/vm/drop_caches'
sudo sh -c 'echo 3 >/proc/sys/vm/drop_caches'

Use free to check the memory & usage.

Figure Display

feh <image_name>

Pause a Running Process and Run in Background

ctrl-z
$ bg

bg command moves jobs to the background, as if they had been started with &.

Run a Job Remotely (ssh) and Then Exit

$ nohup long-running-process &
$ nohup command1 > /dev/null 2>&1 &
$ nohup command1 > output.log 2>&1 &
$ exit

Cron Job

https://phoenixnap.com/kb/set-up-cron-job-linux

DNS Not Working

Check the status of systemd-resolved and restart it if needed:

sudo systemctl status systemd-resolved.service
sudo systemctl restart systemd-resolved.service

If you have error sudo: unable to resolve host meta: Temporary failure in name resolution, check if the host name has been set properly:

ubuntu@meta:~/owk-actions$ cat /etc/hostname
meta
ubuntu@meta:~/owk-actions$ cat /etc/hosts
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Here we need to add an extra line 127.0.1.1 meta to the file so it should looks like this:

ubuntu@meta:~/owk-actions$ cat /etc/hosts
127.0.0.1 localhost
127.0.1.1 meta

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Compression and Decompression

tar -czvf archive_name.tar.gz /path/to/folder
  • tar: This is the command to create or extract tar archives.
  • c: This option tells tar to create a new archive.
  • z: This option instructs tar to compress the archive using gzip compression.
  • v: This option makes tar output verbose information, showing the files being compressed.
  • f: This option specifies the filename for the archive.
  • archive_name.tar.gz: This is the name you want to give to the compressed archive file, with the .tar.gz extension indicating that it's a gzipped tar file.
  • /path/to/folder: This is the path to the folder you want to compress. Replace it with the actual path on your system.
tar -xzvf archive_name.tar.gz
  • x: This option tells tar to extract the files from the archive.
  • z: This option instructs tar to decompress the archive using gzip compression.
  • v: This option makes tar output verbose information, showing the files being extracted.
  • f: This option specifies the filename of the archive.