Unix Help File Notes

Unix Commands all ECE Grad Students Should Know

• Very basic commands (many csh or tcsh commands)
  • cd
  • ls -l -L -R -t -1
  • history
  • alias
  • !<command_number>
  • !<beginning characters of previous command line>
  • !!
  • <new_command> !$
  • <command_1> | <command_2>
  • <command_1> | <command_2> > <output_file>
  • set
  • setenv
  • su
  • find
  • directory: .
  • directory: ..
  • directory: ~
  • directory: /
• File handling commands
  • cat
  • less -Mq
  • more
  • tail
  • head
  • chmod
  • chgrp
  • ln -s
• File processing commands
  • grep
  • fgrep
  • egrep
  • sort
  • diff
  • tkdiff
  • sed
  • awk
  • wc
• System commands
  • top
  • nice
  • renice 19 1234     # new priority 19, PID 1234
  • ps
  • jobs
  • kill
  • <ctrl> z     # To suspend a job
  • bg         # For backgrounding jobs
  • df
  • du
  • w
  • finger

  • Try this the next time all computers must be shutdown: open an xterm window for every computer then paste and hit return on all shutdown commands at the same time. Otherwise, some computers hang and can not be shutdown (this happened with pizza) when other computers are brought down first.

    Or try this: 1) shutdown all computers which do not share drives with other machines, then 2) shutdown file servers (pizza, pepper, cookie) simultaneously.

  • To shutdown a linux computer:

    1. Never ever shut down a machine unless you are sure no one is logged in. In fact, do not reboot machines unless it is really necessary. It is seldom necessary to reboot. Let support@ece know before you reboot. The only exception is if the 110V building power is off and the machine is running from its UPS power supply.

    2. Before shutting down pizza, always check first if the proposed time is ok with support@ece and give at least one day notice to all users including users in other groups (e.g., Raj's). Bringing down pizza may hang machines that mount pizza's partitions and require that they be rebooted also.

    3. Type   w   and   finger   to check for other users.

    4. Type   top   to check for running programs.

    5. Type   ps -aux | less   to check for user programs.

    6. Shutdown the machine (results in power off for most machines)

       • To reboot machine in 3 minutes with message for any users possibly missed, and to put reason in system log files.
         sudo /sbin/shutdown -r +5 'Machine going down for [reason]'      

       • To shutdown machine in 3 minutes with message for any users possibly missed, and to put reason in system log files.
         sudo /sbin/shutdown -h +5 'Machine going down for [reason]'      

       • Shutdown now only when 110V building power is off (and machine is running from its UPS).
         sudo /sbin/shutdown -h now 'Shutting down because power is off'      

    7. In all cases, watch the console screen for important messages. In most cases, the machine will power off by itself. When you are certain the shutdown is complete, press the power button once (if off) or twice (once off, once on) to restart the machine.

• General but less common commands

  • cvs
  • spell, ispell
  • uniq
  • groups <user_name>

Good computer habits and etiquette

• Write text files (documents, code, etc.) with no more than 80 columns of text. Many people use multiple 80-column terminals side by side and wider columns are very annoying.

Notes on various things

Public & private key authentication with SSH.
  
1. Run "ssh-keygen -t rsa -b 1024", enter a password if you like.
   Just press enter to have no password for authentication.  This
   generates two files, "id_rsa" (private key), and "id_rsa.pub"
   (public key).  By default these will be in "~/.ssh/".
2. Copy the the contents of "id_rsa.pub" into the file
   "~/.ssh/authorized_keys2" on the remote system.
   Ex: "cat id_rsa.pub >> ~/.ssh/authorized_keys2"
3. Copy "id_rsa" to "~/.ssh" on your local system if not already
   there.
   (Append if it's already there?)
4. Now simply login using "ssh user@host" and a password will no
   longer be required unless you set a password on your key files.
   (What are the "key files" and how is a password set on them?)
 
WARNING: Protect your private key by keeping it in a safe location.
Someone who has your private key can login as you without a password,
even if you change your password.  If this happens you will have to
generate a new public/private key pair and follow these steps again.