General Red Hat Linux Information

A Few Things to Remember

1. When you su to Root, _your_ environment is exported (still active) so things like $PATH are unchanged.
2. Use su - to get the environment to match the new user ID. This will send you to the new ID's home dir.
3. You can use su -c "command_string_in_quotes" if you only want to run one command as root.
4. If you stop the network with /etc/rc.d/init.d/network stop it also stops lo, the local loopback interface.
5. If you run ps without any switches, it only shows processes running in _that_ shell. Use ps -ea for all ps's
6. If you appear to lock the system while experimenting you can usually avoid a reboot by trying one of:
   • ctr-alt-F1 will show the X server output, alt-F7 to return to X
   • ctr-alt-F2 (F2 to F6) to a new console. Try to kill the problem process.
   • if your home dir is on an NFS server, and it disappears, (from playing with pump) restart the network with "/etc/init.d/network stop" then ...start.
   • try to ssh or telnet into the system if either service runs on that system.
   • ctr-alt-backspace will kill X

Useful Commands:

• dd -copy a file or image to another file or device. (use to copy a boot image to a floppy disk)
• df -shows filesystem use by partition    -use df -i for inode useage
• du -shows disk usage of each FILE, recursively for directories
• dump -backup files or filesystems
• fdformat -low level format a floppy disk
• fdisk -like everyone else's, but more in depth
• fsck -check and repair a Linux file system
• mkbootdisk -mk stands for make, you figure it out. (standard modular kernels only)
• mkfs -build a Linux File System, usually on a hdd
• restore -restores data from dump archive
• taper -front end for dump and restore (can probably set to other utils)

• alias -creates a shortcut for a command
• awk -extract fields from data
• bg -sends a job to the background
• cat -create, combine or display contents of files
• cd -change directory. With no arguments it changes to your HOME directory
• chattr -change file or directory attributes
• chgrp -change file or directory group membership
• chmod -change file or directory privileges
• chown -change file or directory ownership
• cmp, comm, diff -compare contents of files
• cp -copy a file or directory
• exec -replaces the running process with a new one
• exit n -quits the shell with exit status n
• expand -convert tabs to spaces
• export -makes variables available to spawned shells
• fg n -brings job n to the foreground
• find -search for files within a specified directory hierarchy
• grep, egrep, fgrep -searches directory or file contents. -use to include or exclude strings
• head, tail -display beginning or end of a file. also monitor and display changes
• jobs -lists all jobs (background and suspended)
• less -buffers screen output and allows scrolling up or down
• ln -create either a hard or symbolic link to a file or directory
• locate -locate a file anywhere on the system (use with grep to filter results)
• lsattr -list file or directory attributes
• ls -list directory contents
• merge -incorporates changes from two separate working files into a third (original) file
• mkdir -make a directory
• more -displays output one screen at a time. But less is much more!
• mv -move a file or directory
• paste -combine two files line by line (file1_line1 + file2_line1 = file3_line1)
• pico -an easier, less powerful, text editor. A good choice to start with
• Piping, I/O and error redirection to control output
  • a Pipe or | allows the output of one command to be sent as input to another
  • redirect input, output or error messages with < or >
  • a semicolun seperates commands, running them sequentially
• pwd -print working directory (aka: "where the heck am I?")
• rm -remove a file or directory
• rmdir -remove a directory
• sed -edit and substitute fields from data
• sort -sort lines within text files
• tar, compress, gzip, zcat -used for file compression and decompression
• tr -manipulates single or multiple characters
• unexpand -convert spaces to tabs
• vi -the best text editor. (Actually it is usually alliased to 'vim' "vi improved")
• wget -quick command to download files from web and ftp sites (binary mode)
• which -shows first occurrence of filename in users path. This is the one that will execute

• ctl u -clear left from cursor (also works in most programs)
• ctl k -clear right from cursor (also works in most programs)
• ctl e -move cursor to end of text (also works in most programs)
  
  
• ctl s -put shell to sleep
• ctl q -wake the sleeping shell
• ctl p -previous command (like up arrow)
• ctl n -next command (like down arrow)
• ctl "any other character" -causes some other action (or not)

• dig -send domain name query packets to name servers
• host -DNS lookup utility
• ifconfig -displays or manipulates the network interfaces
• ifdown -use to stop a singe active interface, as opposed to using /etc/ini.d/network stop
• ifup -use to activate a singe interface, as opposed to using /etc/ini.d/network start
• netconf -configure networking
• netconfig -set up networking
• netstat -lots of info re routing, etc.
• nslookup -get information from name servers (replaced by host or dig)
• pump -configure net interface using DHCP protocol
• tcpdump -dumps all tcp traffic to screen
• whois -retrieves info on domains by name, also see whois.arin.net for lookup via IP

• chkconfig -lists and changes services started from init.d scripts
• dmesg -displays the contents of what scrolls by during boot (run level 2?)
• free -memory and system information
• kill -kill a process
• ps -shows running processes
• pstree -displays processes in tree form
• rpcinfo -report RPC information. To display all RPC services registered on the local machine use: rpcinfo -p
• tail -displays last part of file
• telinit -use to send signal to init, such as change run levels. Kind of a user interface to init
• top -displays status of most active processes
• updatedb -updated the data base used for "locate" and possibly others
• vigr -same as vipw but edits the group file.
• vipw -a safer way to edit the password file. It locks the /etc/passwd, opens it in vi, and when done, unlocks it and updates any related files.

• a2ps -convert ascii files for printing on a PostScript printer
• lpr -send a file to a printer
• mpage -print multiple pages per sheet
• ps2pdf -Convert PostScript files to PDF

• apropos -searches man page "Description" field for keyword
• crontab -automates commands by running a configured times. Read man pages for cron and crontab.
• date -display or manipulate system date and time.
• id -shows your UID and GID, handy to clearify when using su
• last -shows logon history
• mail -a mail utility
• man n manpage-name -will go to the man page referenced in other man pages. eg."see crontab(5)"
• man man -information on using the manual help pages. Try mam -K keyword to search all man pages.
• rpm -qa |grep partial_package_name -this will show which version RPM app. is installed
• su -change your UID to a second user, by default change to Root
• time -time since the Epoch (00:00:00 UTC, January 1, 1970), measured in seconds. This could be used to calculate elapsed time between events.
• useradd -add a new user to the system (root only)
• users -shows who is logged onto that host
• w -shows who is logged on and what they are doing

• The system wide startup file is /etc/rc.local
• Most startup scripts run from /etc/rc.d/init.d/ use chkconfig to control them
• The user specific file is $HOME/.bash_profile
• System wide environment and startup programs are in /etc/profile
• System wide functions and aliases go in /etc/bashrc
• To change your startup shell edit /etc/passwd. The last entry is the shell.

• The system wide aliases are in /etc/bashrc
• The user specific aliases are in $HOME/.bashrc


• The files are self explanitory.
  To create a command called lsl that is equivilent to ls -aFl|less, add the line:
  alias lsl='ls -aFl|less'
  Now when you run lsl it is the same as entering ls -aFl | less