Manage processes

$systemctl enable/disable nginx = enables/disables nginx to start/stop at boot time

$systemctl start/stop nginx = starts/stops nginx in the current time

$systemctl reload serviceName = re-read program configuration file without killing the process

$systemctl daemon-reload = reload daemon after every service configuration change

$htop = lists all running processes

$ps aux --sort=-%mem | head = This will show you top 10 process that using the most memory $ps -ef = lists all user processes

$ps aux | grep -i firefox = find firefox PID so you can kill process if needed (kill PID)

$kill $! = kill the most recently backgrounded job

$kill $(ps -A -ostat,ppid | awk '/[zZ]/{print $2}') = kill all zombie processes

Other commands to send processes to background, bring process to foreground, kill, etc:

https://unix.stackexchange.com/questions/104821/how -to-terminate-a-background-process/104825

$sudo apparmor_parser -r /etc/apparmor.d/usr.sbin.mysqld = reloads apparmor usr.sbin.mysqld profile when mysql server does not start

$sar -r = monitor CPU, RAM, I/O etc.

Display kernel messages from boot time

$dmesg | grep -i error = print the error message buffer of the kernel

$dmesg | grep -i warn

$dmesg = print messages produced by the device drivers. The boot process generates a particularly dense stream of kernel mess ages.

Find username and process and kill

$who | grep username (to get the pts/# terminal) = check all username connections to the server and kill the process with next command

$sudo pkill -f pts/#

$ps -aux | grep 'nano' = finds the PID and user that uses the 'nano' application

$kill -9 PID = force (-9) kills specified PID

Fix DNS

$sudo apt-get remove --purge resolvconf && sudo apt-get install --reinstall resolvconf = uninstall and re-install resolvconf

Search file/directory/program on hard drive

$grep -E --color wordToFind /path/To/file = searches and highlights the wordToFind inside of a file

$which date = shows you where the program “date” is located so you can pass that path into your script when you call that pro gram

$locate -i interfaces = searches for file "interfaces" on hard drive (on root folder and subfolders)

$find . -type d -exec chmod 755 {} \; = search in current location (.) for type “directory” and execute chmod to change permissions to 755 for everything inside directory

$find . -type f -exec chmod 644 {} \; = search in current location (.) for type “file” and execute chmod to change permissions to 644 for all files

$sudo find / |grep "\.pem" = search for all files with extension pem on root folder /

$find / -name fileNameOrPartOf\* -print = search for fileNameOrPartOf with wildcard at the end (use escape \ for *) in top root \ folder and print results

$grep appNameInstalled /var/log/apt/history.log = find time/date appNameInstalled was installed on server

$zgrep appNameInstalled /var/log/apt/history.log.2.gz = searches through the archived log file

$sudo apt list --installed = lists all installed packages

$sudo apt remove package-name = uninstalls package-name

Permanently enable timestamp for 'history' command:

$echo'HISTTIMEFORMAT="%d/%m/%y %T "'>> ~/.bashrc = for e.g. “29/02/99 23:59:59”

$echo'HISTTIMEFORMAT="%F %T "'>> ~/.bashrc = for e.g. “1999-02-29 23:59:59”

$source~/.bashrc

Diff command:

diff is a command-line utility that allows you to compare two files line by line. It can also compare the contents of directories. The diff command is most commonly used to create a patch containing the differences between one or more files that can be applied using the patch command.

$diff -qrc tx2_june01.csv all.csv

$diff -c tx2_june01.csv all.csv

$diff -U 0 all.csv tx2_june01.csv | grep ^@ | wc -l

$diff -U all.csv tx2_june01.csv | grep ^@ | wc -l

$diff all.csv $tx2_june01.csv | grep ^@ | wc -l

$diff all.csv tx2_june01.csv | wc -l

$ls -al all.csv tx2_june01.csv

$wc -l tx2_june01.csv

$wc -l all.csv

$sudo nano all2.csv