Syntax and usage of Linux commands
Command	Use / Syntax	Remarks
useradd	useradd -d /home/name -n username	create user and home directory
usermod	usermod oldacc -l newacc	change account name    old/new
	usermod olddir -l newdir	change directory name   old/new
	usermod -G group,group,group..n username	puts user in named groups
groupmod	groupmod -n newgroupname oldgroupname	changes group name       new/old
newgrp	newgrp promnix	change current group to promnix
chown	chown peter filename	give peter ownership of file
chgrp	chgrp promnix filename	give promnix group rights to file
chmod	chmod ugo=rwx filename	change permissions of file to all rwx
chage	chage -E 2002/05/13	account expires 13 May 2002
passwd	passwd -l name	locks account by adding !
passwd	passwd john	changes john's password
userdel	userdel -r name	remove user and home dir files
groupadd	groupadd groupname	add new group
groupdel	groupdel promnix	remove promnix group if ok
rpm	rpm --rebuilddb	rebuilds RPM database
	rpm -ivh samba-2.08-12mdk.i386.rpm	installs samba [-Uvh upgrades]
	rpm -qi samba	queries rpm database re samba
	rpm --rebuild samba-2.08-14mdk.i386	rebuilds a binary package from source
	rpm -e samba-2.08-14mdk.i386	uninstall package
dpkg	dpkg --install package	installs package
	dpkg -P samba	purges / removes package (also -r)
alien	alien --to-rpm program-1.2.3-i386.deb	convert debian package to rpm
apt-get	apt-get update	debian web based update of packages
tar	tar -cvf backupfile.tar filenames	creates archive in xxx.tar format
	tar -cvf /dev/st0 filenames	archive to tape
	tar -xvf backupfile.tar	extracts files from archive
mount	mount -w -t ext2 /dev/sda3 /mnt/scsi	mount in write mode the 3rd scsi partition
"	mount -t ext2 -o rw /dev/sda3 /mnt/scsi	mount in write mode the 3rd scsi partition
"
smbclient	smbclient //hertz/peter	connect to hertz and have ftp type rights
smbmount	smbmount //hertz/peter /mnt/xxxx	mount a remote share for copying etc
chkconfig	chkconfig --list         [also ntsysv and tksysv]	list services at each runlevel
"	chkconfig --level 3 smb on	enable samba at runlevel 3
fdisk	"fdisk /dev/had"	check partition information for ide drive 1
mkfs	"mkfs -t ext2 /dev/hda"	format ext2 fstype for ide drive
mt	mt -f /dev/st0 fsf 1	move tape head by 1 count [of files}
gdb	gdb - c core	analyse core dump
du	du -h --max-depth=2	check disk usage down to 2 dir levels
df	df -h	check disk space usage, human readable
ps	ps -u tynan	show process status for user tynan
nice	nice -n -15 process1	increase the priority of process1
kill	kill -s 15 2304	closes down process 2304 via shutdown
killall	killall processnameX	terminates all processnameX
free	free -m -s 10	check memory in megabytes every 10 sec
dd	dd if=/dev/zero of=swap.swp bs=1024 count=10000	create an empty swap file
mkswap	mkswap /swap.swp	format the file as a swap partition
swapon	swapon /swap.swp	turn the swap file on for use
lpq	lpq -Pdeskjet	checks the print queue of deskjet
lpr	lpr -Pdeskjet filename	prints filename to remote printer deskjet
lprm	lprm 4506	removes job 4506 as listed by lpq
lpc	lpc -Pdeskjet stop [also start, up, down, enable...]	stops printing to deskjet
lsmod	lsmod	check which kernel modules are loaded
hdparm	hdparm -t /dev/hdb	test harddrive transfer rates
dmesg	dmesg | grep eth0	shows the kernel boot up info for eth0
setserial	setserial -a /dev/Stty1	show comm2 settings, resource use
ifconfig	ifconfig eth0	show ethernet0 address and status
route	route -n	show routing info with 0.0.0.0 as default
fsck	fsck /dev/hdb	file system check hard drive 2
lsof	lsof	list of open files
ping	ping 192.168.1.100	test connection to address on network
traceroute	traceroute 192.168.1.200	check path to destination
find	find -name filename -print	find all files = filename
locate	locate filename	finds file if in database
whereis	whereis util	searches /bin directories for util
grep	grep pattern files	searches files for pattern
more	more filename  [or less filename]	scrolls file contents with page stops
cat	cat filename > destination	sends file contents to destination