Daemons
From Linux Shell Scripting Tutorial - A Beginner's handbook
A daemon (also known as background processes) is a Linux or UNIX program that runs in the background. Almost all daemons have names that end with the letter "d". For example, httpd the daemon that handles the Apache server, or, sshd which handles SSH remote access connections. Linux often start daemons at boot time. Shell scripts stored in /etc/init.d directory are used to start and stop daemons.
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Typical functions of daemons
- Open network port (such as port 80) and respond to network requests.
- Monitor system such as hard disk health or RAID array.
- Run scheduled tasks such as cron.
List of service daemons for Linux and Unix-like systems
- amd - Auto Mount Daemon
- anacron - Executed delayed cron tasks at boot time
- apmd - Advanced Power Management Daemon
- atd - Runs jobs queued using the at tool
- autofs - Supports the automounter daemon allowing mount and unmount of devices on demand
- crond - The task scheduler daemon
- cupsd - CUPS printer daemon
- dhcpd - Dynamic Host Configuration Protocol and Internet Bootstrap Protocol Server
- ftpd - FTP Server Daemon
- gated - routing daemon that handles multiple routing protocols and replaces routed and egpup
- httpd - Web Server Daemon
- inetd - Internet Superserver Daemon
- imapd - An imap server daemon
- lpd - Line Printer Daemon
- memcached - In-memory distributed object caching daemon
- mountd - mount daemon
- mysql - Database server daemon
- named - A DNS server daemon
- nfsd - Network File Sharing Daemon
- nfslock - Used to start and stop nfs file locking services
- nmbd - Network Message Block Daemon
- ntpd - Network Time Protocol service daemon
- postfix - A mail transport agent used as a replacement for sendmail
- postgresql - Database server daemon
- routed - Manages routing tables
- rpcbind - Remote Procedure Call Bind Daemon
- sendmail - A mail transfer agent Daemon
- smbd - Samba (an SMB Server) Daemon
- smtpd - Simple Mail Transfer Protocol Daemon
- snmpd - Simple Network Management Protocol Daemon
- squid - A web page caching proxy server daemon
- sshd - Secure Shell Server Daemon
- syncd - Keeps the file systems synchronized with system memory
- syslogd - System logging daemon
- tcpd - Service wrapper restricts access to inetd based services through hosts.allow and hosts.deny
- telnetd - Telnet Server daemon
- vsftpd - Very Secure FTP Daemon
- webmin - Web based administration server daemon
- xinetd - Enhanced Internet Superserver Daemon
- xntd - Network Time Server Daemon
How do I start / stop / restart daemons for the shell prompt?
You need to use the service command as follows[1][2]::
service daemon-name-here start service daemon-name-here stop service daemon-name-here restart
In this example, start, stop, and restart httpd daemon:
service httpd start service httpd stop service httpd restart
Sample outputs:
How do I see list of all running daemons?
To see the status all installed daemons, enter:
service --status-allSample outputs from CentOS Linux development server:
acpid (pid 3914) is running... anacron is stopped atd (pid 4433) is running... auditd (pid 3537) is running... automount (pid 4174) is running... Avahi daemon is not running Avahi DNS daemon is not running hcid (pid 3821) is running... sdpd (pid 3827) is running... collectl is stopped conmand is stopped cpuspeed is stopped crond (pid 4386) is running... cupsd is stopped dc_client is stopped dc_server is stopped dnsmasq is stopped dovecot is stopped dund is stopped gpm (pid 4372) is running... hald (pid 4094) is running... hidd (pid 4144) is running... httpd is stopped irattach is stopped irqbalance (pid 3686) is running... iscsid (pid 2775) is running... iscsid (pid 2775) is running... Kdump is not operational krb524d is stopped libvirtd is stopped lighttpd is running for example.com domain. lighttpd is running for example.net domain. mcstransd (pid 2932) is running... memcached (pid 39605) is running... dbus-daemon (pid 3802) is running... multipathd is stopped mysqld (pid 4319) is running... named (pid 21265) is running... netplugd is stopped Configured devices: lo br0 br1 eth0 eth1 Currently active devices: lo eth0 eth1 br0 br1 NetworkManager is stopped rpc.mountd is stopped nfsd is stopped mcstransd (pid 2932) is running... mdadm is stopped mdmpd is stopped memcached (pid 39605) is running... dbus-daemon (pid 3802) is running... multipathd is stopped mysqld (pid 4319) is running... named (pid 21265) is running... rpc.mountd is stopped nfsd is stopped rpc.rquotad is stopped rpc.statd is stopped nscd is stopped ntpd (pid 4240) is running... pcscd (pid 3905) is running... sendmail (pid 4354) is running... setroubleshootd (pid 3813) is running... smartd (pid 4491) is running... smbd is stopped nmbd is stopped snmpd (pid 4191) is running... squid (pid 13123) is running... openssh-daemon (pid 4217) is running... syslogd (pid 3563) is running... klogd (pid 3566) is running... tux is stopped vsftpd is stopped winbindd is stopped wpa_supplicant is stopped xfs (pid 4418) is running... xinetd (pid 4229) is running... ypbind is stopped yum-updatesd (pid 4525) is running...
Sample outputs from my Ubuntu Linux desktop systems:
[ ? ] acpi-support [ ? ] acpid [ ? ] alsa-mixer-save [ ? ] anacron [ + ] apache2 [ + ] apparmor [ ? ] apport [ ? ] arpwatch [ ? ] atd [ ? ] aumix [ + ] bind9 [ ? ] binfmt-support [ + ] bluetooth [ - ] bootlogd [ ? ] bridge-network-interface [ - ] brltty [ ? ] console-setup [ ? ] cron [ + ] cups [ ? ] dbus [ ? ] dmesg [ ? ] dns-clean [ ? ] failsafe-x [ - ] fancontrol [ ? ] gdm [ - ] grub-common [ ? ] gssd [ ? ] hddtemp [ ? ] hostname [ ? ] hwclock [ ? ] hwclock-save [ ? ] idmapd [ ? ] irqbalance [ ? ] iscsi-network-interface [ - ] kerneloops [ ? ] killprocs [ ? ] libvirt-bin [ - ] lighttpd [ - ] lm-sensors [ + ] memcached [ ? ] module-init-tools [ ? ] mysql [ + ] net-acct [ ? ] network-interface [ ? ] network-interface-security [ ? ] network-manager [ ? ] networking [ ? ] ondemand [ + ] open-iscsi [ ? ] pcmciautils [ ? ] plymouth [ ? ] plymouth-log [ ? ] plymouth-splash [ ? ] plymouth-stop [ ? ] portmap [ + ] postfix [ ? ] pppd-dns [ ? ] procps [ + ] pulseaudio [ ? ] qemu-kvm [ ? ] rc.local [ ? ] resolvconf [ ? ] rpc_pipefs [ - ] rsync [ ? ] rsyslog [ - ] saned [ ? ] screen-cleanup [ ? ] sendsigs [ - ] smartmontools [ ? ] speech-dispatcher [ + ] ssh [ ? ] statd [ ? ] stop-bootlogd [ ? ] stop-bootlogd-single [ + ] sysstat [ ? ] udev [ ? ] udev-finish [ ? ] udevmonitor [ ? ] udevtrigger [ ? ] ufw [ ? ] umountfs [ ? ] umountnfs.sh [ ? ] umountroot [ ? ] unattended-upgrades [ - ] urandom [ + ] vmware [ + ] vnstat [ - ] wicd [ + ] winbind [ ? ] wpa-ifupdown [ - ] x11-common
See also
References
