Daily often used commands under Linux (Ubuntu)

This is a list of my daily often used commands under Ubuntu Linux server and desktop. It's for the people like me who do not have a good memory. I hope it will save you a lot of time if you have this list near at hand and mostly don't need to search a command online anymore. The comments before every command are not trying to explain every option in the command. If you have any question about the options please see the --help or man manuals.

There are a lot of other tricks to use the commands or combinations of the commands. If you want to add your often used commands in the list, please fork this and make Pull Request. I'm still trying to update the list if I have some time.

Enjoy the list!

Fortunately I have the root privileges mostly. So the most of the following commands don't have a sudo prefix.

User administration

# create an user with home-dir
useradd -o -m -s /bin/bash/ username

# create a super user, make him the SAME user as root and have home-dir
# (BUT BE CAREFUL OF DOING THIS ENLESS YOU KNOW WHAT YOU ARE DOING)
# to delete this super user: change the uid from 0 to other in the /etc/passwd
useradd -u 0 -g 0 -o -m -s /bin/bash username 

# change the password of an user	
passwd username

# disable login for an user; sudo -u -i still works
passwd -d username

# delete an user and his home-dir
userdel -r username  

# add a group (with --system is a system group)
addgroup groupname  

# add an user to a group
usermod -a -G groupname username

# delete an user from a group
gpasswd -d username groupname

# show log of users' login
last -a

# show all users' name, id, sh/bash
cat /etc/passwd

# show all groups' name, id, assigned users
cat /etc/group

# login remote server without entering password
ssh-keygen -t rsa -f keyFileName_rsa
ssh-copy-id -i keyFileName_rsa.pub username@remote
ssh username@remote

# copy file content to clipboard
cat fileName | xclip -sel clip

APT and dpkg stuffs:

# update apt repository data
apt-get update

# install a package with version number
apt-get install abc=5.5.29...
dpkg -i *.deb

# search a package with name
apt-cache search packagename

# uninstall a package
apt-get remove packagename
dpkg -r packagename

# show information about a package
apt-cache showpkg packagename

# compare the version of a package in the apt repository and local
apt-cache policy packagename

# CLI-gui for apt
aptitude

# show a list of upgradeable packages on the machine
apt-get -u upgrade

# upgrade only one package
apt-get install --only-upgrade packagename

# search a package that contains the given file or command on the machine
dpkg -S file/command

# list all installed packages
dpkg -l

# search packages that contain the given file name (can be non-installed)
apt-file search filename 

# delete downloaded files of installation (to free some spaces on disk)
apt-get autoclean 

# PPA install:
add-apt-repository ppa:user/ppa-name
apt-get update
apt-get install packageInThePPA

# list all packages in one PPA
grep ^Package /var/lib/apt/lists/ppaname	

### backup installed packages and restore in another machine
# create a backup of currently installed packages:
dpkg --get-selections > packagesList
# restore installations from the list packagesList:
dpkg --clear-selections
dpkg --set-selections < packagesList
apt-get autoremove
apt-get dselect-upgrade

Port forwarding over SSH:

# Let's say, I want through local port 3316 to connect 3306 on example.org with username: 
ssh -f username@example.org -L 3316:localhost:3306 -N

Ubuntu-Destop running in VirtualBox under Windows:

# auto setup the resolution to the size of the VM-window in the host(Windows)

# in 12.04
apt-get install virtualbox-ose-guest-utils virtualbox-ose-guest-x11 virtualbox-ose-guest-dkms

# in 14.04
apt-get install virtualbox-guest-dkms

Windows-Desktop running in VirtualBox under Ubuntu:

# auto setup the resolution to the size of the VM-window in the host(Ubuntu)
# get the name of the running vm
VBoxManage list runningvms 
VBoxManage controlvm "name_of_the_running_vm" setvideomodehint 1280 900 32 

Setup the number of workspaces in Ubuntu : 3*3

dconf write /org/compiz/profiles/unity/plugins/core/hsize 3
dconf write /org/compiz/profiles/unity/plugins/core/vsize 3
restart

# actually I don't use the above mentioned 3 commands any more because I found 
# the unity tweak tool.	
apt-add-repository ppa:tualatrix/ppa
apt-get update
apt-get install ubuntu-tweak

Operations for files or directories:

# create dir
mkdir abc

# remove empty dir and its parents (a, b und c will be all deleted)
rmdir -p a/b/c 

# remove non-empty dir
rm -fr abc

# rename dir
mv dirname newdirname

# copy dir (if target exists, copy the file in the target dir)
cp -r path/to/sourcedir path/to/targetdir

# create file
touch filename

# copy file
cp path/to/sourcefile path/to/targetfile

# move file
mv path/to/sourcefile path/to/target

# rename file
mv filename newfilename

# show list of all files and dirs in current location with permissions and human-readable size
ls -alh

# permissions: read = 4, write = 2, execute = 1
# example: -rw-r--r--  ==> 644

# modify permissions of a dir and its children
chmod -R 777 dirname

# modify owner of a file or dir
chown uid filename

# modify group of a file or dir
chgrp groupname filename

# make new files and directories in one directory also having the same group
chmod g+s dirname

# search files or dirs that contain 'abc' in name
find -name '*abc*'

# search files that contain 'abc' in contents
find . -name '*' | xargs grep 'abc'
# or
fgrep -nr somethingToSearch *.*

# sort files by last changed time
find -type f -exec stat --format '%y %n' "{}" \; | sort -nr | head -n 100

# replace strings in all found files using regular expression
find -type f -name "*" -exec sed -i 's/someStringsToBeReplaced/somethingNew/g' {} \;

# file monitoring
tail -f filename

# show the disk usage of files and dirs in current location
du -ah --max-depth=1 ./

# show total disk usage of a dir
du -sh path/to/dir

# sort files and dirs by disk usage in current location
du -sh * | sort -h

# upload a dir to a remote machine
rsync -zrp(tg -X) /path/to/a user@remote.host.com:/path/to/b/

# download dir from another machine
scp -r user@hosturl:/path/to/dir /path/to/local/dir

# download file from web
wget file-URL

# compress tar.gz
tar -zcf abc.tar.gz dirnameOrFilename

# extract tar.gz
tar -zxf abc.tar.gz

# show list of files in a tar.gz
tar -tvf abc.tar.gz

# extract one file from a tar.gz
tar -zxf abc.tar.gz path/to/filename	

System and machine:

# if I forgot every sudo-users' passwords and cannot enter the machine:
# restart the maschine, enter "Recovery Mode" and type:
mount -o remount,rw /

# add path to evironment PATH for this login session
export PATH=$PATH:/my/path

# show enironment variables
env

# show the version of operation system
uname -a; head -n 1 /etc/issue

# show info about CPU
cat /proc/cpuinfo

# show mounted devices
mount | column -t

# list of pci devices
lspci -tv

# list of usb devices
lsusb -tv

# show info about memory, cache and swap in MB, update every 10 seconds
free -m -s 5

# show info about file system
df -ahT

# show info about network interfaces
ifconfig

# show info about firewalls
iptables -L

# show info about listened ports (protocol, connections, status, processes)
netstat -plant

# scan the status of a port (remote)
nmap -p 8080 example.com

# monitor net transfer for processes
nethogs

# show info about running processes
ps -ef
ps -eaux

# sort processes by current cpu usage using ps
ps -eaux | sort -k 3

# sort processes by current mem usage using ps
ps -eaux | sort -k 4

# monitor running processes
top

# limit top by specific process-name
top -p `pgrep processName | tr "\\n" "," | sed "s/,$//"`

# calculate ram usage of processes that contain the same processName
top -n1 -b | grep processName | sort -u -rk 9 | awk '{print $10}' | sed "s/,/\./" | paste -sd+ - | bc

# check errors of system or services
systemctl status serviceName
journalctl -xe

Execution of commands:

# scheduling tasks:
# @reboot @yearly ... @daily commands
# or
# 30 2 * * * commands (this means, execute the commands at 2:30 every day)
crontab -e

# show scheduled tasks
crontab -l

### some methods to record output
# record all output to a file
command > output.txt
# record all output to a file (append)
command >> output.txt
# record stderr to a file
command 2> output.txt
### record output of some commands to a file without sh-file
script output.txt
command1
command2
command3
exit
### record commands and their outputs and replay that
# record commands and outputs
script -t 2>commands.time output.txt
command1
command2
command3
exit
# replay the commands (nothing will be re-executed, only the typing and results)
scriptreplay commands.time output.txt

Often used programs' commands:

Git:

# init a new repository
git init
# init a new repository on server-site
git init --bare

# add github, bitbucket, ... to existing local git-repo
git remote add origin ssh://git@bitbucket.org/.../...git
git push -u origin master

# commit changes
git commit -a -m "commit comments"

# recursive add empty directories to git-repository, except the directories in .git/
find . -type d -empty -not -path "./.git/*" -exec touch {}/.gitkeep \;

# show branches
git show-branch

# create branch and switch to it
git checkout -b branchName

# delete branch
git branch -d branchName

# merge other branch with current branch
git merge otherBranchName

# use stash to store changes temporarily
git stasch
git stash list
git stash apply [stash@{num}]

Apache2:

# start, stop
service apache2 start/stop

# restart gracefully
service apache2 reload

# enable, disable modules
a2enmod modName
a2dismod modName

# enable, disable sites
a2ensite siteName
a2dissite siteName

# enable, disable config
a2enconf confName
a2disconf confName

# show enabled modules or sites(settings in config files)
apache2tcl -M / -S

OpenSSL:

Docker:

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