LinuxGem

# cheat_sheet.org.sh
# The contents of this file are released under the GNU General Public License. Feel free to reuse the contents of this work, as long as the resultant works give proper attribution and are made publicly available under the GNU General Public License.
# Best viewed in emacs org-mode.
# Alternately, one can keep this cheat sheet handy by adding the following line to ~/.bashrc:
#
# alias cheatsheet="less ~/path_to_cheat_sheet.org.sh" 


* Reference:
** Basics:
*** Getting help:

# View the manual for target command
man command

# Get help with a target command (probably the same as above, but not always):
command -h

# In case you forget the name of a command, print possible commands relating to any given word:
apropos word

# View index of help pages:
info

*** Command Line Utilities:
**** Basic File and Directory Operations:

# Recurse into subdirectories and list those as well:
ls -R

# List files by modification time, most recent first.
ls -lt

# Mount filesytem:
mount /dev/device_name /media/device_name

# Unmount:
umount /media/device_name

# Forensically clone filesystems and do other low-level operations on files. Be careful with this one. Can be destructive:
dd

# Work with disk partitions:
parted

# Filesystem creation tool:
mkfs

**** System Administration:

# Execute command as an administrator (can be destructive/insecure. Use only for system administration tasks):
sudo command

# Become system administrator:
sudo -s

# Quit system administration:
exit

# Forgot to type sudo in front of a command and already hit enter? Repeat the last command using sudo:
sudo !!

***** Installing software from a .tgz (also known as a tarball):

# First, unzip the tarball (see section on tar, below)
# Next, move into unzipped directory:
cd software_directory

# Always read README first if it is provided, in case there are any modifications to the procedure outlined below:
cat README

# Automatically check for appropriate configurations and generate a MAKE file in the directory:
./configure

# Compile software. May require sudo:
make

# Move files into their appropriate locations. May also require sudo:
make install

# Clean up files in directory, in case make command fails, or just to remove unnecessary cruft:
make clean

***** Ubuntu/Debian Software repositories:

# Check distro repositories for software updates:
sudo apt-get update

# Download and install updates (update first):
sudo apt-get upgrade

# Search for package in the repositories:
apt-cache search keyword

# Get more detail on one specific package:
apt-cache show package_name

# Download and install a package:
sudo apt-get install package_name

# View the output of a command in a more convenient format:
command | less

**** Working With Files:

# Print a file in terminal:
cat file

# Find files matching filename:
locate filename

# See the version of a program or the location of the program
which appname

# Search through filename for matches to phrase:
grep phrase filename

# Search through output of a command for phrase:
command | grep phrase

**** Working With Processes:

# List all running processes:
ps -e

# Standard system monitor showing a more extensive view of all processes and system resources:
top

# Like top, but with a better, cleaner interface:
htop

# Stop a process from using all system resources and lagging computer:
renice process_name

# Kill misbehaving process (use sparingly, last resort, try 'renice' command first):
pkill process name

# Start a process in the background
command &

# Start a process in the background and have it keep running after you log off
nohup command &

**** Compression and Encryption:

# Make a simple compressed backup of files or directories:
tar -cvzf backup_output.tgz target_files_or_directories

# Open a compressed .tgz or .tar.gz file:
tar -xvf target.tgz

# Encrypt a file:
gpg -o outputfilename.gpg -c target_file

# Decrypt a file:
gpg -o outputfilename -d target.gpg

# Zip and encrypt a directory simultaneously:
gpg-zip -o encrypted_filename.tgz.gpg -c -s file_to_be_encrypted

*** The Bash shell:
**** File Name expansions:
# Current user's home directory:
~/

# Current directory:
./

# Parent directory:
../

# Or even (Two parent directories down):
../../

# All files in target directory. (Be very careful.):
/*

**** Output Redirects:

# Redirect output of one command into the input of another with a pipe:
command_1 | command_2

# Or even:

command_1 | command_2 | command_3

# Redirect output to a file:
command > file

# Or:

file > file

# Or even, to redirect in a different direction:
file < file

# Append output rather than writing over the target file:

file_or_command >> file

# Works like |, but it writes output to both target and terminal:
tee target

# Redirect standard output and error to /dev/null, where it is deleted.
command > /dev/null 2>&1

**** Controlling Execution:
# Wait until command 1 is finished to execute command 2
command_1 ; command_2

# Or even:
command_1 ; command_2 ; command_3

# && acts like ; but only executes command_2 if command_1 indicates that it succeeded without error by returning 0.
command_1 && command_2

# || acts like && but only executes command_2 if command_1 indicates an error by returning 1.
command_1 || command_2

**** Bash Wildcards:
# Zero or more characters:
*

# Matches "phrase" and any number of trailing characters:
phrase*

# Matches any incidences of "phrase" with any trailing or leading chars:
*phrase*

# Matches any one char:
?

# Matches any of the characters listed inside brackets:
[chars]

# Matches a range of chars between a-z:
[a-z]

** Advanced:
*** Command Line Utilities, Continued:
**** Networking:

# Configure network interfaces:
ifconfig

# Configure wireless network interfaces:
iwconfig

# Connect to a remote server.
ssh username@ip_address

# Forward X from target to current machine (Get a remote desktop. Somewhat obscure, but very useful):
ssh -X username@ip_address

# Copy files/directory over the network from one machine to another recursively:
scp -r source_filename:username@ip_address target_filename:target_username@target_ip_address

# Copy only changes between files or directories (super efficient way to sync directories, works either locally or with remote servers using username@ip_address:optionalport, just like ssh):
rsync source target

# Check to see if target is online and responding
ping ip_address

# View network route to target:
traceroute6 ip_address

# Network Monitor
netstat

# View firewall rules
iptables -L

# Scan this machine(localhost) to check for open ports:
nmap localhost

***** wget:

# download a file over http:
wget http://example.com/folder/file 

# complete a partially downloaded file:
wget -c http://example.com/folder/file

# start download in background:
wget -b wget -c http://example.com/folder/file

# download a file from ftp server:
wget --ftp-user=USER --ftp-password=PASS ftp://example.com/folder/file

***** netcat:

# Listen for input from network on recieving_port, dump it to a file (insecure, but handy):
netcat -l recieving_port > file_copied

# Pipe the output of a command to a target ip and port over the network:
command | netcat -w number_of_seconds_before_timeout target_ip target_port

# Use tar to compress and output a file as a stream, pipe it to a target ip and port over the network:
sudo tar -czf - filename | netcat -w number_of_seconds_before_timeout target_ip target_port

**** Users and Groups:
# Change owner of a file or directory:
chown user_name:group_name directory_name

# Change privileges over file or directory (see man page for details.)
chmod

# Create a new user:
adduser

# Change user privileges (be very careful with this one):
usermod

# Delete user
deluser

# Print groups:
groups

# Create a new group:
groupadd

# Change group privileges:
groupmod

# Delete group:
delgroup

# Temporarily become a different user:
su username

# Print usernames of logged in users:
users

# Write one line to another user from your terminal:
talk

# Interactive talk program to talk to other users from terminal (must be installed from repositories.):
ytalk

**** Working With Files, Continued:
# View what processes are using what files:
lsof

# View the differences between two files:
diff file_1 file_2

# Output the top number_of_lines of file:
head -n number_of_lines file

# Like head, but it outputs the last -n lines:
tail -n number_of_lines file

# Checksum a file:
md5sum file

# Checksum every file in a directory (install this one from repositories.):
md5deep directory

# Checksum a file (better algorithm with no hash collisions):
sha1sum

# Same operation as md5deep, but using sha1:
sha1deep

# Call command every few number_of_seconds, and highlight difference in output:
watch -d -n number_of_seconds command

# Execute command, print how long it took:
time command

# View files in directory from largest to smallest:
du -a directory | sort -n -r | less

# remove spaces from filenames in current directory:
rename -n 's/[\s]/''/g' *

# change capitals to lowercase in filenames in current directory:
rename 'y/A-Z/a-z/' *

***** Environment and Hardware:
# print motherboard information
dmidecode

# Print full date and time:
date

# Print the hostname of this machine:
echo $HOSTNAME

# Print information about current linux distro:
lsb_release -a

# Or even:

more /etc/issue

# Print linux kernel version:
uname -a

# Print information about kernel modules:
lsmod

# Configure kernel modules (never do this ;p ):
modprobe

# View Installed packages:
dpkg --get-se