Linux Services, Devices, and Deamons

Linux Startup Services:

Startup services are services run at boot time. They may be provided by daemon programs running in the background or are one time only programs run during the bootup to provide some function to the system. This section gives a brief overview of these services. This section outlines those services that can be started using Redhat's linuxconf program. Not all are necessarily daemon programs. Also it is possible to set up other startup programs, daemons, or services that are not included in this list. There are 3 basic categories to these services.

  • A one time only program run at bootup to provide a function to the system such as kudzu, or keytable.
  • A program run as a daemon upon startup that provides system services such as gpm, autofs, cron, and atd.
  • A program run as a daemon upon startup that provides networking services such as dhcpd, bootparamd, arpwatch, gated, and httpd.
amd Runs the automount daemon for remote filesystem mounting such as nfs.
apmd Monitors battery status and can shut down the system if power is low.
arpwatch Keeps track of ethernet IP address parings what are resolved using the ARP protocol. This allows system administrators to note new IP addresses being used. It maintains a database in /var/arpwatch/arp.dat.
atd Runs commands scheduled by the "at" program at their scheduled times. Jobs are stored in /var/spool/at
autofs Also called the automount daemon, it is used to automatically mount filesystems on demand. It is especially worthwhile for working with removeable media such as floppies or CD ROM disks.
bootparamd Allows remote computers to boot from a Linux box using the BOOTP network protocol. This allows the remote computer to get its IP address if the server knows the hardware address of the remote machine. The DHCP protocol is an upgrade to this protocol since it is more automated.
crond A daeman that executes scheduled commands according to the /etc/crontab file. It can be used to clean up temporary files in /tmp and /var/tmp and other places.
dhcpd Provides DHCP services to "lease" out IP addresses to remote machines.
gated Provides routing services for BGP and other protocols. Alternative to routed. Supports IGP (Interior gateway protocol) and EGP (Exterior Gateway Protocol).
gpm Provides mouse support to Linux.
httpd The Apache hypertext transfer protocol Web server.
identd Server implementing the TCP/IP proposed standard IDENT user identification protocol in RFC 1413. It returns user information to a remote host that a user is requesting a service from. Also called auth.
inet The internet super daemon (inetd) that provides all the services specified in /etc/inetd.conf.
innd The Usenet news server
isdn Provides ISDN (networking interface) services. See the isdnctrl man page for more information. The isdnctrl program is used to set up isdn interfaces. Pertinent files are /etc/sysconfig/activeisdn, /dev/isnnctrl, /etc/sysconfig/provider, and /var/log/isdn.log.
keytable Loads the appropriate keyboard map from /etc/sysconfig/keyboard. This does not set up a daemon program to reside in the background, but just loads the keyboard keytable and the system font.
kudzu Detects and configures new or changed hardware on a system. This program is run once when the system boots and does not run as a daemon in the background.
ldap Lightweight directory access protocol package which provides client/server based directory database services which runs on UNIX platforms over TCP/IP. RFC is 1777.
linuxconf According to Redhat it is a post startup hook for linuxconf. It does not run as a daemon.
lpd Provides printing services to Linux. It is a print spooler daemon.
mars-nwe Loads the MARS Netware compatible file and print server daemon called nwserv. Allows a Linux machine to be used as a file and printserver for netware based clients using IPX/SPX.
mcserv Allows users on remote machines to use the midcommander file manager to work with files. It uses the PAM library for authentication.
named Provides DNS services. It is a name server used to translate local IP addresses to names and vice-versa.
netfs Mounts and unmounts Network Fils System (NFS), Windows (SMB), and Netware (NCP) file systems. The mount command is used to perform this operation and no daemon is run in the background.
network Brings up all the network interfaces under the directory /etc/sysconfig/network-scripts. Also controls IP_forwarding and IP_defrag.
nfs Provides Network File System server services
nfslock NFS file locking service. Starts the daemons rpc.locked and rpc.statd. The rpc.statd daemon implements the Network Status Monitor (NSM) RPC protocol which is a reboot notification service used to implement file lock recovery when an NFS server crashes and reboots.
nscd The name switch cache daemon. which handles password and group lookups for running programs and caches the information for the next query. Normally this daemon is used to support NIS.
pcmcia Provides access to PCMCIA (PC Cards) services configured in the /etc/exports file.
portmap Provides Remote Procedure Call (RPC) support for other protocols like NFS.
postgresql Runs the postgres database and provides SQL services. It runs the daemon postmaster.
pulse Heartbeat daemon for monitoring the health of lvs (Redhat clustering services) cluster nodes. This tool is used for clustering machines.
pxe A preboot execution environment (PXE) server. Allows network boot of other PXE machines. PXE is a standard developed by Intel for a means of booting various operating systems on remote machines.
random Saves and restores a random value used to generate better random numbers for security. No daemon program is invoked for this operation.
routed Provides for automatic router table updates using the RIP dynamic routing information protocol.
rstatd The rstat protocol allows users on a network to get performance information for any machine on the network. Runs the rpc.rstatd daemon which provides performance statistics retrieved from the kernel usually by using the "rup" command.
rusersd Provides services that allow users to find one another over the network.
rwalld Provides users with an ability to use the rwall command to write messages on remote terminals.
rwhod The rwho protocol lets remote users get a list of all users logged onto a machine by running the rwho daemon.
sendmail The sendmail mail transport agent daemon used to move e-mail from one machine to another.
smb Provides SMB (Samba) client/server services which include file and print services. It allows Linux computers to exchange file and printer services with Microsoft Windows based systems.
snmpd Provides Simple Network Management Protocol support to Linux.
squid Runs the squid proxy web server
syslog System logging daemon which records system events to log files usually in the directory "/var/log". The actual name of the daemon is klogd.
xfs X font file server
xntpd Starts the Network Time Protocol NTPv3 daemon. NTP provides a means to synchronize time and coordinate time distribution in a large, diverse internet operating at all speeds. RFC 1305 describes this protocol.
ypbind Binds YP/NIS clients to a yellow pages server. NIS (Network Information Service) is a name service created by Sun.
yppasswdd Allows users to change their passwords on systems running YP/NIS
ypserv This daemon provides the YP/NIS (Network Information System) server functions.

Linux Deamons

This section gives a brief overview of miscellaneous daemons (not covered in the paragraph on services) running on the system and their function.

init The first process to start after the kernel. It controls the system runlevel and adapts any child whose parent dies.
nmbd Responds to netbios name service requests for Samba works in conjunction with Samba which is why it is not mentioned under startup services..
update (kupdate) Does a sync every 30 seconds. A sync is an updating of memory pages, or virtual memory pages that have been changed, but not saved to the swap disk
bdflush (kflushd) Started by update - does a more imperfect sync more frequently
getty Listens for connections at terminals