Various commands for system and third-party Unix/Linux programs.
ab -n 100 -c 50 -k -H 'Accept-Encoding: gzip,deflate' url- Test the connectivity of a host (requires Apache)
adduser user group- Add an existing user to a group
alias- Show currently set command aliases
command arg1 arg2 &- Send a command to the background by postfixing it with an ampersand
sudo /etc/init.d/apache2 restart- Restart apache
apt-cache show packageNameHere- Show info about an installed package
sudo apt-get update- Update repositories list and find any software upgrades
sudo apt-get upgrade- Update packages with updates available
aspell -c filename- Check a file for spelling errors.
bg- Send current foreground process to the background. Press control + z first to suspend the running process
cat file1.txt file2.txt > file3.txt- Reads file1.txt and file2.txt and combines those files to make file3.txt.
cat id_rsa.pub >> authorized_keys- Appends file on left to file on right
ccsm- Start Compiz config manager
chgrp group file- Change group of file or directory
sudo chmod o+x /home- all executing for a directory, which is necessary for access by Apache
sudo find /path/to/someDirectory -type d -print0 | xargs -0 sudo chmod 755- Set all directories under a specific directory to 755
sudo find /path/to/someDirectory -type f -print0 | xargs -0 sudo chmod 644- Set all files under a specific directory to 644
crontab -e- edit user's crontab file
crontab -l- view user's crontab file
crontab -u user -l- View another user's crontab file
sudo crontab -l- View root's cron file
curl -C url- Resume a previous download
curl -H "header: value" url- Request URL with a custom header
curl -I host- See request data for a host
curl -i url- Include response headers in the output
curl url -O- Save download using name from URL
curl url -o filename- Save download to filename
date --date="string"- Convert some data string to a standardized date string. Can be specific date or relative (e.g. yesterday)
date --date=@timestamp- Convert unix timestamp to date
date -u- Display date/time in Universal Time
dd if=/dev/urandom of=/dev/diskOrPartition bs=1M- Overwrite disk or partition with random bits
dd if=/dev/zero of=/dev/diskOrPartition bs=1M- Overwrite disk or partition with zeros
df -h- Show file system usage in human-readable format
dig -x ip_address- Do a reverse domain lookup by IP
dig @dns-server host- Get DNS record for host from a specific dns server (e.g. 8.8.8.8 for Google's)
dig host- Get DNS record for a given host
dpkg --get-selections- Show installed packages
du -h- Show sizes of directories in human-readable format
du -s- Show just a summary of directory's size
env- Show currently set environment variables
export variable=value- Assigns a value to a variable for the current session. Variable can be used in subsequent commands with $variable. Can be made permanent by adding command to a file like .bash_profile
sudo fdisk -l- List hard drive info and all partitions
fg job_ID- Bring a process running in the background to the foreground
file -i file_name- Show text encoding of a file
find -iname "file_name"- Same as -name, but case-insensitive
find -name ""file_name"- Find file in current directory and its subdirectories
find -name "file_name" -exec command {} \;"- Execute a command on files found, where {} represents the file
find -name "file_name" -type type- Filter found files by type (f for file, d for directory)
find . -type f | wc -l- Count number of files under current directory
free -m- Show amount of used and free memory in megabytes
fusermount -u ~/yourmountdirectory- Unmount a remote SSH directory
gedit- open file for editing in gedit
gpg --allow-secret-key-import --import private_key- Import private key into keyring
gpg --armor --detach-sig file- Sign a file, creating a separate signature file
gpg --armor --export --output file.gpg user_or_key- Export public key to a file for sharing
gpg --armor --export-secret-key --output file.gpg user_or_key- Export private key to a file
gpg --gen-key- Generate a gpg public/private key pair
gpg --import public_key- Import public key into keyring
gpg --list-keys- List public keys in your keyring
gpg --output out_file --decrypt in_file- Decrypts file to new file
gpg --sign --encrypt --recipient recipient_name file- Sign and encrypt a file with a recipient's public key in one step
gpg --sign file- Sign a file
gpg --verify file.asc file- Verify a signed file with a separate signature file
gpg --verify file.gpg- Verify a signed file
gpg -r <keyID> --multifile --encrypt- Encrypt all files in directory
gpg -r key_id --encrypt in_file- Encrypt file, specifying key ID with -r
grep -e "regex" path- Search using extended regex (same as egrep)
grep -r string directory- Search recursively in a directory for a string
groupadd group- Create a new user group
sudo grub-set-default number- Set default OS in Grub to the specified number, starting with zero
htop- Improved UI for viewing and controlling processes (may need installation)
id user- See info about a user, including groups it's in
ifconfig- List details of each network connection (eth0, etc.)
jobs -l- List processes running in the background, along with process IDs
jpegtran -optimize image.jpg > image.jpg-opt && mv image.jpg-opt image.jpg- Optimize a jpg and replace original with output
kill PID- End a process based on its process ID
ln -s target shortcut- Create a symbolic link
ls -lsa- Show everything (hidden too) with details
lsof -P -i -n- Show programs that are accessing the Internet
lspci- List all PCI devices
lspci -k- List all PCI devices and the drivers that are handling them
lspci | grep VGA- See your video card
lsusb- List all USB devices
md5sum file- Get the md5 hash of a file
sudo mkdir -p /media/cdrom- Example of mounting an ISO (1)
mke2fs -c /dev/sdxx- Check a partition for bad blocks
mkfs -t type /dev/sdxx- Make a filesystem of the given type on the given partition
mount- View all mounts
mount -M current_directory new_directory- Move a mount point
mount -t iso9660 -o ro /dev/cdrom /mnt- Mount a cd-rom (also works for an ISO)
mount /dev/device- Mount a device, checking fstab for its mount directory
mount directory- Mount to a directory, checking fstab for its mount device
sudo mount -o loop ~/Desktop/ubuntu-10.10-alternate-i386.iso /media/cdrom- Example of mounting an ISO (2)
sudo mount -t fs-type -o uid=username,gid=username device directory- Mount a device, specifying filesystem type and user/group
mysqldump -u user -p database_name > dumpfilename.sql- Create a database backup from MySQL
netstat -a --numeric-ports | grep 8321- tell if a port is in use
netstat -plantu- Show all listening and established ports TCP and UDP together with the PID of the associated process
nmap host_or_ip- Scan a host or IP for networking info (e.g. open ports)
passwd- Change your password
passwd user- Change another user's password
patch -p1 < patch_file- Apply a patch
patch -R < patch_file- Undo an applied patch
pgrep name- Search for a running process by name
popd- Change back to the last directory saved with pushd
ps -A- Show all running processes
ps -u user- Show all processes running under user
ps aux --sort -rss- Sort processes by memory usage, descending
sudo -u postgres psql- Enter PostgreSQL CLI as root user.
pstree- View running processes based on which processes started which
pushd directory- Change to a directory, saving the previous directory to go back to
python -m SimpleHTTPServer- Start dev web server serving from the current directory
renice priority PID- Change the priority of a currently running process
rm -rf /tmp/foo- Recursively remove directories and files
rmdir /tmp/foo- Remove directory
rsync -rlztv source target- Sync files recursively, preserving symlinks, using compressing, preserving modification times, and providing verbose output
scp- copy file to or from remote computer over SSH
scp -r- copy a directory, including any subdirectories
scp myfile user@host:DestinationFolder- Copy to specific location on server
sed -i "s/original/new/g" file- Replace all instances of original with new in file. i = save to same file; s = substitute
sudo sh -c 'cat ~/id_rsa.pub >> authorized_keys'- Run cat as sudo
echo -n somePassword | sha256sum- Get the SHA (256 bit) hash of a string via echo, with -n to prevent extra \n
sha256sum file- Get the SHA (256 bit) hash of a file
shred --remove --iterations=50 file- Overwrite file with random bits using 50 passes, removing file afterwards
sudo shutdown -h now- Immediately shuts down computer
ssh -D local_port -C user@host -p ssh_port- Create proxy tunnel for web browsing
ssh user@host -o TCPKeepAlive=yes- Helps keep connection alive during long operations over ssh (e.g. rsync)
ssh-keygen -C comment- Create an SSH key with a custom comment
sshfs username@host:/remotepath ~/yourmountdirectory- Mount a remote directory via SSH
stat file- Show file stats, including size and ownership
tar -cvzf archive.tar.gz fileOrDirectory- Create a gzipped tarball of a file or directory; c = create a tar; z = use gzip; f = read from specified file
tar -zxvf archive.tar.gz- Open/uncompress gzipped tarball; z = use gzip; x = extract to disk; v = verbose; f = read from specified file
top- Dynamically display running processes
umount -f directory- Forcefully unmount a mount
umount directory -l- Unmount a mount once it is no longer busy
sudo update-grub- Update Grub bootloader after modifying /etc/default/grub
useradd -g group -d home_directory -s login_shell user- Create a new user, specifying its group, home directory, and login shell
usermod -a -G group user- Add a user to a group
usermod -g group -d home_directory -s login_shell user- Modify an existing user, specifying its group, home directory, and login shell
vi- edit file in vi editor
sudo visudo- Safely opens /etc/sudoers for editing
w- Show currently logged in users
which command- Show the location of a command's source file