Linux Know-How provides a collection of introductory texts on often needed Linux skills.

Some Linux Daemons

Daemons are "resident"programs that periodically wake up, check your system and may perform certain functions. They do not take any input and don't normally produce any output. Your Linux system is likely set to run quite a number of daemons. Most of them can be (dis)selected by running the program ntsysv (RedHat) as root and checking the appropriate box. The short description of each daemon is available under netsysv by pressing <F1>. If the daemon you need is not listed in ntsysv, you need to insert your RedHat/Mandrake installation CD and install the appropriate package. The alternative to ntsysv may be tksysv (type as root, in X terminal), which is perhaps more flexible, but way more complicated (it lets you set up the list of daemons to run in each runlevel). Another, simpler and even more powerful+flexible+difficult-to-use tool is /sbin/chkconfig.

Here is a short list of popular daemons with a brief description:

anacron - checks `cron' jobs that were left out due to down time and executes them. Useful if you have cron jobs scheduled but don't run your machine all the time--anacron will detect that during bootup.

amd - automount daemon (automatically mounts removable media).

apmd - Advanced Power Management BIOS daemon. For use on machines, especially laptops, that support apm.

arpwatch - keeps watch for ethernet/ip address pairings.

atd - runs jobs queued by the "at" command.

autofs - control the operation of automount daemons (competition to amd).

bootparamd - server process that provides information to diskless clients necessary for booting.

crond - automatic task scheduler. Manages the execution of tasks that are executed at regular but infrequent intervals, such as rotating log files, cleaning up /tmp directories, etc.

cupsd - the Common UNIX Printing System (CUPS) daemon. CUPS is an advanced printer spooling system which allows setting of printer options and automatic availability of a printer configured on one server in the whole network. The default printing system of Linux Mandrake.

dhcpd - implements the Dynamic Host Configuration Protocol (DHCP) and the Internet Bootstrap Protocol (BOOTP).

gated - routing daemon that handles multiple routing protocols and replaces routed and egpup.

gpm - useful mouse server for applications running on the Linux text console.

httpd - daemon for the Apache webserver.

inetd - listens for service requests on network connections, particularly dial-in services. This daemon can automatically load and unload other daemons (ftpd, telnetd, etc.), thereby economizing on system resources. Newer systems use xinetd instead.

isdn4linux - for users of ISDN cards.

kerneld - automatically loads and unloads kernel modules.

klogd - the daemon that intercepts and displays/logs the kernel messages depending on the priority level of the messages. The priority is (copied from /usr/include/linux/kernel.h ):

KERN_EMERG "<0>" system is unusable

KERN_ALERT "<1>" action must be taken immediately

KERN_CRIT "<2>" critical conditions

KERN_ERR "<3>" error conditions

KERN_WARNING "<4>" warning condition

KERN_NOTICE "<5>" normal but significant condition

KERN_INFO "<6>" informational

KERN_DEBUG "<7>" debug-level messages

The messages typically go to the appropriately named files in the directory /var/log/kernel.

kudzu - detects and configures new or changed hardware during boot.

keytable - loads selected keyboard map.

linuxconf - the linuxconf configuration tool. The automated part is run if you want linuxconf to perform various tasks at boot time to maintain the system configuration.

lpd - printing daemon.

mcserv - server program for the Midnight Commander networking file system. It provides access to the host file system to clients running the Midnight file system (currently, only the Midnight Commander file manager). If the program is run as root the program will try to get a reserved port otherwise it will use 9876 as the port. If the system has a portmapper running, then the port will be registered with the portmapper and thus clients will automatically connect to the right port. If the system does not have a portmapper, then a port should be manually specified with the -p option (see below).

named - the Internet Domain Name Server (DNS) daemon.

netfs - network file system mounter. Used for mounting nfs, smb and ncp shares on boot.

network -activates all network interfaces at boot time by calling scripts in /etc/sysconfig/network-scripts .

nfsd - used for exporting nfs shares when requested by remote systems.

nfslock - starts and stops nfs file locking service.

numlock - locks numlock key at init runlevel change.

pcmcia - generic services for pcmcia cards in laptops.

portmap - needed for Remote Procedure Calls. Most likely, you need it for running network.

postfix - mail transport agent which is a replacement for sendmail. Now the default on desktop installations of Mandrake (RedHat uses sendmail instead).

random - saves and restores the "entropy" pool for higher quality random number generation.

routed - daemon that manages routing tables.

rstatd - kernel statistics server.

rusersd, rwalld - identification of users and "wall" messaging services for remote users.

rwhod - server which maintains the database used by the rwho(1) and ruptime(1) programs. Its operation depends on the ability to broadcast messages on a network.

sendmail - mail transfer agent. This is the agent that comes with Red Hat.

smbd - the SAMBA (or smb) daemon, a network connectivity services to MS Windows computers on your network (hard drive sharing, printers, etc).

squid - An http proxy with caching. Proxies relay requests from clients to the outside world, and return the results. You would use this particular proxy if you wanted to use your Linux computer as a gateway to the Internet for other computer on your network. Another (and probably safer at home) way to do it, is to set up masquarading.

syslogd - manages system activity logging. The configuration file is /etc/syslog.conf .

smtpd - Simple Mail Transfer Protocol, designed for the exchange of electronic mail messages. Several daemons that support SMTP are available, including sendmail, smtpd, rsmtpd, qmail, zmail, etc.

usb - daemon for devices on Universal Serial Bus.

xfs - X font server.

xntpd - finds the server for a NIS domain and stores the information about it in a binding file.

ypbind - NIS binder. Needed if computer is part of Network Information Service domain.

Last Update: 2010-12-16