Useful Unix Commands

This is a bookmark-able reference to commonly used commands in Unix-like environments.

tar

Basic tar commands. Remember this one?

tar czf file.tar.gz <files> # create a tarball
tar xzf file.tar.gz         # extract a tarball

dd

Useful for creating files of arbitrary size with pseudorandom content.

dd if=/dev/urandom of=target-file bs=1M count=10

if is the input file, of is the output file, and bs is the block size. count is number of blocks to read from if and write to of.

split

Splitting files. Use -d for numeric suffixes.

split -b 8K <file> <prefix-name>    # split a file into 8kb chunks
split -n 128 <file>                 # split a file into 128 chunks

scp

Basic copy syntax. Use -r for copying directories recursively.

scp -i path_to_secret.pem local_file.txt remote_username@10.10.0.2:/remote/directory
scp -i path_to_secret.pem remote_username@10.10.0.2:/remote/file.txt /local/directory
scp user1@host_1.com:/files/file.txt user2@host_2.com:/files

ssh

Generate an RSA SSH key:

ssh-keygen -t rsa -b 2048 -C "foo@bar.com"

SSH config example Host block

# ~/.ssh/config

Host <name>
  Hostname <ipv4>
  User <user>
  Port <port>
  IdentitiesOnly <yes/no>
  IdentityFile <path_to_secret>

To proxy using a bastion host, use the following directive in the config.

  ProxyCommand ssh -W %h:%p <name-of-jump-server> 

# Add an SSH key to authentication agent

ssh-add -K ~/.ssh/id_rsa

# ~/.ssh/config (bg SSH session with port forwarding
# e.g. running remote jupyter notebooks)

Host foo
  Hostname <ipv4>
  User <user>
  IdentityFile <path_to_secret>

$ ssh -NfL 9999:localhost:8888 foo

psql

Common PostgreSQL slash commands

 \l         # list databases
 \c orders  # switch to database 'orders'
 \dt        # list tables
 \conninfo  # echo connection info
 \des       # list foreign servers
 \dew       # list foreign data wrappers
 \?         # get meta-command help

Connect to a PostgreSQL database

psql -h <host> -p <port> -d <db> -U <user>