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