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File System
ls — list items in current directory
ls -l — list items in current directory and show in long format to see perimissions, size, and modification date
ls -a — list all items in current directory, including hidden files
ls -F — list all items in current directory and show directories with a slash and executables with a star
ls dir — list all items in directory dir
cd dir — change directory to dir
cd .. — go up one directory
cd / — go to the root directory
cd ~ — go to to your home directory
cd - — go to the last directory you were just in
pwd — show present working directory
mkdir dir — make directory dir
rm file — remove file
rm -r dir — remove directory dir recursively
cp file1 file2 — copy file1 to file2
cp -r dir1 dir2 — copy directory dir1 to dir2 recursively
mv file1 file2 — move (rename) file1 to file2
ln -s file link — create symbolic link to file
touch file — create or update file
cat file — output the contents of file
less file — view file with page navigation
head file — output the first 10 lines of file
tail file — output the last 10 lines of file
tail -f file — output the contents of file as it grows, starting with the last 10 lines
vim file — edit file
alias name 'command' — create an alias for a command
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System
shutdown — shut down machine
reboot — restart machine
date — show the current date and time
whoami — who you are logged in as
finger user — display information about user
man command — show the manual for command
df — show disk usage
du — show directory space usage
free — show memory and swap usage
whereis app — show possible locations of app
which app — show which app will be run by default
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Process Management
ps — display your currently active processes
top — display all running processes
kill pid — kill process id pid
kill -9 pid — force kill process id pid
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Permissions
ls -l — list items in current directory and show permissions
chmod ugo file — change permissions of file to ugo - u is the user's permissions, g is the group's permissions, and o is everyone else's permissions. The values of u, g, and o can be any number between 0 and 7.
7 — full permissions
6 — read and write only
5 — read and execute only
4 — read only
3 — write and execute only
2 — write only
1 — execute only
0 — no permissions
chmod 600 file — you can read and write - good for files
chmod 700 file — you can read, write, and execute - good for scripts
chmod 644 file — you can read and write, and everyone else can only read - good for web pages
chmod 755 file — you can read, write, and execute, and everyone else can read and execute - good for programs that you want to share
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Networking
wget file — download a file
curl file — download a file
scp user@host:file dir — secure copy a file from remote server to the dir directory on your machine
scp file user@host:dir — secure copy a file from your machine to the dir directory on a remote server
scp -r user@host:dir dir — secure copy the directory dir from remote server to the directory dir on your machine
ssh user@host — connect to host as user
ssh -p port user@host — connect to host on port as user
ssh-copy-id user@host — add your key to host for user to enable a keyed or passwordless login
ping host — ping host and output results
whois domain — get information for domain
dig domain — get DNS information for domain
dig -x host — reverse lookup host
lsof -i tcp:1337 — list all processes running on port 1337
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Searching
grep pattern files — search for pattern in files
grep -r pattern dir — search recursively for pattern in dir
grep -rn pattern dir — search recursively for pattern in dir and show the line number found
grep -r pattern dir --include='*.ext — search recursively for pattern in dir and only search in files with .ext extension
command | grep pattern — search for pattern in the output of command
find file — find all instances of file in real system
locate file — find all instances of file using indexed database built from the updatedb command. Much faster than find
sed -i 's/day/night/g' file — find all occurrences of day in a file and replace them with night - s means substitude and g means global - sed also supports regular expressions
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Compression
tar cf file.tar files — create a tar named file.tar containing files
tar xf file.tar — extract the files from file.tar
tar czf file.tar.gz files — create a tar with Gzip compression
tar xzf file.tar.gz — extract a tar using Gzip
gzip file — compresses file and renames it to file.gz
gzip -d file.gz — decompresses file.gz back to file
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Shortcuts
ctrl+a — move cursor to beginning of line
ctrl+f — move cursor to end of line
alt+f — move cursor forward 1 word
alt+b — move cursor backward 1 word