Section 2.1. Common Commands

2.1. Common Commands

Following are lists of commonly used system administration commands.

2.1.1. Clocks

Command	Action
hwclock	Manage hardware clock.
rdate	Get time from network time server.
zdump	Print list of time zones.
zic	Create time-conversion information files.

2.1.2. Daemons

Command	Action
apmd	Advanced Power Management daemon.
atd	Queue commands for later execution.
bootpd	Internet Boot Protocol daemon.
cupsd	Printer daemon.
fingerd	Finger daemon.
ftpd	File Transfer Protocol daemon.
imapd	IMAP mailbox server daemon.
klogd	Manage syslogd.
mountd	NFS mount request server.
named	Internet domain nameserver.
nfsd	NFS daemon.
pppd	Maintain Point-to-Point Protocol (PPP) network connections.
rdistd	Remote file distribution server.
rexecd	Remote execution server.
rlogind	rlogin server.
routed	Routing daemon.
rpc.rusersd	Remote users server.
rpc.statd	NFS status daemon.
rshd	Remote shell server.
rwhod	Remote who server.
sshd	Secure shell daemon.
syslogd	System logging daemon.
talkd	Talk daemon.
tcpd	TCP network daemon.
tftpd	Trivial File Transfer Protocol daemon.
xinetd	Extended Internet services daemon. Starts other services as needed.
ypbind	NIS binder process.
yppasswdd	NIS password modification server.
ypserv	NIS server process.

2.1.3. Hardware

Command	Action
agetty	Start user session at terminal.
arp	Manage the ARP cache.
cardctl	Control PCMCIA cards.
cardmgr	PCMCIA card manager daemon.
fdisk	Maintain disk partitions.
hdparm	Get and set hard drive parameters.
kbdrate	Manage the keyboard's repeat rate.
ramsize	Print information about RAM disk.
setkeycodes	Change keyboard scancode-to-keycode mappings.
setserial	Set serial port information.
slattach	Attach serial lines as network interfaces.

2.1.4. Host Information

Command	Action
arch	Print machine architecture.
dig	Query Internet domain nameservers.
dnsdomainname	Print DNS domain name.
domainname	Print NIS domain name.
free	Print memory usage.
host	Print host and zone information.
hostname	Print or set hostname.
uname	Print host information.

2.1.5. Installation

Command	Action
cpio	Copy files to and from archives.
install	Copy files into locations providing user access and set permissions.
rdist	Distribute files to remote systems.
tar	Copy files to or restore files from an archive medium.

2.1.6. Mail

Command	Action
fetchmail	Retrieve mail from remote servers.
formail	Convert input to mail format.
mailq	Print a summary of the mail queue.
makemap	Update sendmail's database maps.
newaliases	Rebuild sendmail's alias database.
rmail	Handle uucp mail.
sendmail	Send and receive mail.

2.1.7. Managing Filesystems

To Unix systems, a filesystem is a device (such as a partition) that is formatted to store files. Filesystems can be found on hard drives, floppies, CD-ROMs, USB drives, or other storage media that permit random access.

The exact format and means by which the files are stored are not important; the system provides a common interface for all filesystem types that it recognizes. By default, almost all modern distributions of Linux use a journaling filesystem. When the kernel interacts with a journalling filesystem, writes to disk are first written to a log or journal before they are written to disk. This slows down writes to the filesystem, but reduces the risk of data corruption in the event of a power outage. It also speeds up reboots after a system unexpectedly loses power.

Most current Linux distributions default to the Third Extended (ext3) Filesystem. The ext3 filesystem was developed primarily for Linux and supports 256-character filenames and 4-terabyte maximum filesystem size. This ext3 filesystem is essentially a Second Extended (ext2) filesystem with an added journal. Since it is in all other ways identical to the ext2 system, it is both forward- and backward-compatible with ext2--all ext2 utilities work with ext3 filesystems.

Although not covered in this edition of Linux in a Nutshell, Linux supports three other open source journaling filesystems: IBM's Journaled Filesystem (JFS), SGI's Extensible Filesystem (XFS), and the Naming System Venture's Reiser Filesystem (ReiserFS). In some situations these can be faster than ext3. Some Linux distributions use these alternative filesystems by default. Other common filesystems include the FAT and VFAT filesystems, which allow files on partitions and floppies of Microsoft Windows systems to be accessed under Linux, and the ISO 9660 filesystem used by CD-ROMs.

Command	Action
debugfs	Debug ext2 filesystem.
dosfsck	Check and repair a DOS or VFAT filesystem.
dump	Back up data from a filesystem.
dumpe2fs	Print information about superblock and blocks group.
e2fsck	Check and repair an ext2 filesystem.
e2image	Store disaster-recovery data for an ext2 filesystem.
edquota	Edit filesystem quotas with vim.
fdformat	Format floppy disk.
fsck	Another name for e2fsck.
fsck.ext2	Check and repair an ext2 filesystem.
mke2fs	Make a new ext2 filesystem.
mkfs	Make a new filesystem.
mkfs.ext2	Another name for mke2fs.
mkfs.ext3	Yet another name for mke2fs.
mklost+found	Make lost+found directory.
mkraid	Set up a RAID device.
mkswap	Designate swapspace.
mount	Mount a filesystem.
quotacheck	Audit stored quota information.
quotaon	Enforce quotas.
quotaoff	Do not enforce quotas.
quotastats	Display kernel quota statistics.
raidstart	Activate a RAID device.
raidstop	Turn off a RAID device.
rdev	Describe or change values for root filesystem.
repquota	Display quota summary.
resize2fs	Enlarge or shrink an ext2 filesystem.
restore	Restore data from a dump to a filesystem.
rootflags	List or set flags to use in mounting root filesystem.
setquota	Edit filesystem quotas.
showmount	List exported directories on a remote host.
swapoff	Cease using device for swapping.
swapon	Begin using device for swapping.
sync	Write filesystem buffers to disk.
tune2fs	Manage an ext2 filesystem.
umount	Unmount a filesystem.
warnquota	Mail disk usage warnings to users.

2.1.8. Managing the Kernel

Command	Action
depmod	Create module dependency listing.
lsmod	List kernel modules.
modinfo	Print kernel module information.
modprobe	Load and remove a module and its dependent modules.
sysctl	Examine or modify kernel parameters at runtime.

2.1.9. Networking

Command	Action
ifconfig	Manage network interfaces.
iptables	Administer firewall facilities (2.4 kernel).
named	Translate between domain names and IP addresses.
nameif	Assign names to network devices.
netstat	Print network status.
nfsstat	Print statistics for NFS and RPC.
nsupdate	Submit dynamic DNS update requests.
portmap	Map daemons to ports.
rarp	Manage RARP table.
rndc	Send commands to a BIND nameserver.
route	Manage routing tables.
routed	Dynamically keep routing tables up to date.
rpcinfo	Report RPC information.
ruptime	Check how long remote system has been up.
rwho	Show who is logged into remote system.
traceroute	Trace network route to remote host.
wvdial	Establish dial-up IP connections.

2.1.10. Printing

Command	Action
accept	Tell printer daemon to accept jobs.
lpadmin	Configure printer and class queues.
lpinfo	Show available printers and drivers.
lpmove	Move a print job to a different queue.
reject	Tell printer daemon to reject jobs.
tunelp	Tune the printer parameters.

2.1.11. Security and System Integrity

Command	Action
badblocks	Search for bad blocks.
chroot	Change root directory.

2.1.12. Starting and Stopping the System

Command	Action
chkconfig	Manage which services run in a runlevel.
ctrlaltdel	Shut down, then soft reboot system.
halt	Stop or shut down system.
init	Change runlevel.
reboot	Shut down, then hard reboot system.
runlevel	Print system runlevel.
shutdown	Shut down system.
telinit	Change the current runlevel.
uptime	Display uptimes of local machines.

2.1.13. System Activity and Process Management

A number of additional commands in Chapter 3 are particularly useful in controlling processes, including kill, killall, pidof, ps, and who.

Command	Action
fuser	Identify processes using file or filesystem.
renice	Change the priority of running processes.
top	Show most CPU-intensive processes.
vmstat	Print virtual-memory statistics and process statistics.

2.1.14. Users

Command	Action
chpasswd	Change multiple passwords.
groupadd	Add a new group.
groupdel	Delete a group.
groupmod	Modify groups.
grpck	Check the integrity of group system files.
grpconv	Convert group file to shadow group file.
lastlog	Generate report of last user login times.
newusers	Add new users in a batch.
pwck	Check the integrity of password system files.
pwconv	Convert password file to shadow passwords.
rusers	Print who-style information on remote machines.
rwall	Print a message to remote users.
useradd	Add a new user.
userdel	Delete a user and that user's home directory.
usermod	Modify a user's information.
w	List logged-in users.
wall	Write to all users.
whoami	Show how you are currently logged in.

2.1.15. Miscellaneous

Command	Action
anacron	Schedule commands for periodic execution.
atrun	Schedule commands for later execution.
cron	Schedule commands for specific times.
dmesg	Print bootup messages after the system is up.
ldconfig	Update library links and do caching.
logger	Send messages to the system logger.
logrotate	Compress and rotate system logs.
run-parts	Run all scripts in a directory.