Utilities

Environment Variables {ENV}

Some useful links to explain the concepts of Environment Variables

• https://www.guru99.com/linux-environment-variables.html

• https://www.digitalocean.com/community/tutorials/how-to-read-and-set-environmental-and-shell-variables-on-a-linux-vps

• https://www.slashroot.in/difference-between-bashrc-and-bashprofile

• https://www.cyberciti.biz/faq/linux-list-all-environment-variables-env-command/

Schedulers

Some useful links to cover the working of Crontab and Systemd Timers

Cron Tab

• https://www.thegeekstuff.com/2009/06/15-practical-crontab-examples/

• https://www.cyberciti.biz/faq/linux-show-what-cron-jobs-are-setup/

• https://www.pantz.org/software/cron/croninfo.html

Systemd Timers

• https://opensource.com/article/20/7/systemd-timers

• https://www.neteye-blog.com/2022/12/start-using-systemd-timers-instead-of-cron-anacron/

• https://dev.to/bowmanjd/schedule-jobs-with-systemd-timers-a-cron-alternative-15l8

• https://unix.stackexchange.com/questions/278564/cron-vs-systemd-timers

• https://www.reddit.com/r/linuxadmin/comments/k8l272/systemdtimers_vs_cron/

• https://akashrajpurohit.com/blog/systemd-timers-vs-cron-jobs/

Online Utilities to generate crons

• https://crontab-generator.org/

GREP

Some useful links to cover the working of Grep

• https://thevaluable.dev/grep-cli-guide-examples/

• https://www.linode.com/docs/guides/how-to-use-grep-command/

• https://www.cyberciti.biz/faq/searching-multiple-words-string-using-grep/

• https://www.thegeekstuff.com/2011/10/grep-or-and-not-operators/

• https://www.digitalocean.com/community/tutorials/using-grep-regular-expressions-to-search-for-text-patterns-in-linux

• https://alvinalexander.com/unix/edu/examples/grep.shtml

• https://stackoverflow.com/questions/2427913/how-can-i-grep-for-a-string-that-begins-with-a-dash-hyphen

• https://stackoverflow.com/questions/221921/use-grep-exclude-include-syntax-to-not-grep-through-certain-files

• https://stackoverflow.com/questions/25853722/how-to-suppress-binary-file-matching-results-in-grep

• https://stackoverflow.com/questions/10346816/using-grep-to-search-for-a-string-that-has-a-dot-in-it

Grepping ps output without showing the grep process

• https://www.safaribooksonline.com/library/view/bash-cookbook/0596526784/ch17s18.html

• https://unix.stackexchange.com/questions/74185/how-can-i-prevent-grep-from-showing-up-in-ps-results

FIND

Some useful links to cover the working of Find

• https://thevaluable.dev/find-cli-guide-examples/

• https://www.digitalocean.com/community/tutorials/how-to-use-find-and-locate-to-search-for-files-on-a-linux-vps

• https://tecadmin.net/delete-files-older-x-days/

• https://www.tecmint.com/find-and-sort-files-modification-date-and-time-in-linux/

• https://www.linode.com/docs/tools-reference/tools/find-files-in-linux-using-the-command-line

• https://alvinalexander.com/blog/post/linux-unix/find-how-multiple-search-patterns-filename-command

• https://stackoverflow.com/questions/5475905/linux-delete-file-with-size-0/18052644#18052644

User Management

• https://www.linode.com/docs/tools-reference/linux-users-and-groups

• https://linux-audit.com/unused-linux-users-delete-or-keep/

• https://askubuntu.com/questions/515103/how-can-i-display-all-users-and-groups-with-a-command

• https://askubuntu.com/questions/34074/how-do-i-change-my-username

File Permissions

• https://www.linux.com/learn/getting-know-linux-file-permissions

• https://www.penguintutor.com/linux/file-permissions-reference

• https://www.linux.com/learn/understanding-linux-file-permissions

• https://www.linuxnix.com/chmod-command-explained-linuxunix/

• https://unix.stackexchange.com/questions/21251/execute-vs-read-bit-how-do-directory-permissions-in-linux-work

• https://www.grymoire.com/Unix/Permissions.html

• https://www.thegeekstuff.com/2010/06/chmod-command-examples/

• https://danielmiessler.com/study/unixlinux_permissions/

• https://www.linux.com/learn/how-easily-back-and-restore-linux-file-permissions

• https://unix.stackexchange.com/questions/102286/ls-gives-no-such-file-or-directory-message

Why sudo cd <path-to-dir> doesn’t work

• https://superuser.com/questions/241129/why-wont-sudo-cd-work

• https://askubuntu.com/questions/291666/why-doesnt-sudo-cd-var-named-work

• https://askubuntu.com/questions/468901/how-to-show-only-hidden-files-in-terminal/468902#468902

Sudoers

• https://serverfault.com/questions/364334/test-whether-a-user-has-sudo-privileges-without-requiring-user-input

• https://www.digitalocean.com/community/tutorials/how-to-add-delete-and-grant-sudo-privileges-to-users-on-a-debian-vps

• https://www.thegeekstuff.com/2010/09/sudo-command-examples/

• https://www.garron.me/en/linux/visudo-command-sudoers-file-sudo-default-editor.html

• https://www.digitalocean.com/community/tutorials/how-to-edit-the-sudoers-file-on-ubuntu-and-centos

• https://askubuntu.com/questions/73864/how-to-modify-an-invalid-etc-sudoers-file

• https://askubuntu.com/questions/799669/etc-sudoers-file-corrupted-and-i-cant-run-pkexec-visudo-over-ssh

UserMod Command

• https://www.tecmint.com/usermod-command-examples/

• https://www.crybit.com/15-switches-of-usermod-command-with-example-unixlinux/

• https://muffinresearch.co.uk/linux-changing-uids-and-gids-for-user/

• https://www.smarthomebeginner.com/safely-change-primary-group-group-in-linux/

• https://www.cyberciti.biz/faq/howto-linux-add-user-to-group/

SetUID and SetGID

• https://tutonics.com/articles/linux-file-permissions-chmod-umask/

• https://www.slashroot.in/suid-and-sgid-linux-explained-examples

• https://www.thegeekstuff.com/2013/02/sticky-bit/

• https://www.linuxnix.com/suid-set-suid-linuxunix/

• https://unix.stackexchange.com/questions/28363/whats-the-difference-between-s-and-s-in-ls-la

UMask Values

• → UMask contains default permissions for newly created files / directories based on base permissions for those

• → Base permissions for files is 666 (read-write permissions for owner-group-other : execute permissions are excluded by for files as security measure)

• → Similarly, the base permissions for directories are 777 (read-write-execute permissions for owner-group-other)

• → The UMask values are inverse to regular file permissions → i.e: chmod

• → UMask values = Base permissions - required permissions All UMasks

• https://www.computerhope.com/unix/uumask.htm

• https://www.cyberciti.biz/tips/understanding-linux-unix-umask-value-usage.html

• https://www.digitalocean.com/community/tutorials/linux-permissions-basics-and-how-to-use-umask-on-a-vps

SymLinks

Some useful links to cover the working of SymLinks

• https://www.cyberciti.biz/tips/understanding-unixlinux-symbolic-soft-and-hard-links.html

• https://www.thegeekstuff.com/2010/10/linux-ln-command-examples/

• https://geek-university.com/symbolic-links/

• https://geek-university.com/hard-links/

Others

XArgs vs Exec

• https://danielmiessler.com/blog/linux-xargs-vs-exec/

• https://stackoverflow.com/questions/16758525/make-xargs-handle-filenames-that-contain-spaces

• https://askubuntu.com/questions/666001/piping-find-name-to-xargs-results-in-filenames-with-spaces-not-being-passed-to/666004

NTP

• https://support.ntp.org/Support/TroubleshootingNTP

• https://support.rackspace.com/how-to/using-ntp-to-sync-time/

• https://www.ibm.com/support/knowledgecenter/en/ssw_aix_71/com.ibm.aix.cmds4/ntpdate.htm

Renaming / Deleting multiple files

• https://www.cyberciti.biz/tips/renaming-multiple-files-at-a-shell-prompt.html

• https://www.linux.com/blog/linux-shell-tip-remove-files-names-contains-spaces-and-special-characters-such

• https://www.cyberciti.biz/faq/linux-bash-delete-all-files-in-directory-except-few/

• https://www.tecmint.com/delete-all-files-in-directory-except-one-few-file-extensions/

• https://askubuntu.com/questions/470134/how-to-find-the-creation-time-of-a-file

• https://www.if-not-true-then-false.com/2011/linux-display-show-file-contents-tabs-line-breaks-non-printing-characters/

Rename multiple files with different extensions

• https://superuser.com/questions/865826/linux-mv-command-for-moving-multiple-files-with-different-extensions

Random Tools

• https://aarvik.dk/blacklist-check-unix-linux-utility/

• https://www.tecmint.com/show-progress-linux-commands/

• https://www.tecmint.com/screen-command-examples-to-manage-linux-terminals/

• https://www.thegeekstuff.com/2009/04/chage-linux-password-expiration-and-aging/

• https://www.commandlinefu.com/commands/browse

• https://distrochooser.de/en

• https://www.cyberciti.biz/open-source/command-line-hacks/compgen-linux-command/

• https://www.dynacont.net/documentation/linux/Useful_SystemD_commands/

SysCTL

Some useful links to cover the working of SysCTL

• https://rtcamp.com/tutorials/linux/sysctl-conf

• https://www.cyberciti.biz/faq/linux-kernel-etcsysctl-conf-security-hardening

• https://www.slashroot.in/linux-network-tcp-performance-tuning-sysctl

• https://www.linux.com/news/kernel-tuning-sysctl

LSOF

• https://danielmiessler.com/study/lsof/

• https://catonmat.net/unix-utilities-lsof

• https://www.thegeekstuff.com/2012/08/lsof-command-examples/

• https://unix.stackexchange.com/questions/253321/how-to-display-size-human-readable-in-lsof-grep-var

DIFF

• https://www.lifewire.com/compare-two-text-files-linux-3861434

Comparing difference between files / directories on 2 servers

• https://www.xmodulo.com/how-to-diff-remote-files-over-ssh.html