การทำงานของ Service บน Centos แต่ละตัว

นำมาจาก https://linuxacademy.com/blog/linux/disabling-unused-daemons-to-speed-up-your-boot-sequence/

ตรวจสอบว่า service  ไหนทำงานบน runlevel 5

chkconfig --list | grep “5:on”

สั่งเปิด service บน run level 3 5

chkconfig --level 35 name on

• Bluetooth
  • hcid, sdpd and hidd (These daemons provide Bluetooth services and are unnecessary if you don’t have any Bluetooth hardware)
• Printing
  • cups and cups-config-daemon (These daemons provide printer services and are unnecessary if you don’t have any printer hardware attached to your local pc or to a network pc)
  • hpiod and hpssd (These daemons provide extensive support for HP printers. They can safely be disabled if you never print using an HP printer)
• Console
  • gpm (This daemon provides mouse support for text-based applications, like Midnight Commander. It also provides copying/pasting with the middle mouse button in console environments. Can be disabled if you do not use the console much)
• Webserver
  • httpd (This daemon provides web hosting services, and is unecessary on workstations and servers that do not host any websites or webinterfaces)
  • mysqld and postgresqld (These daemons provide database backend services. You can usually disable them if you’re not running a webserver, although some applications use these databases for their data storage)
• Firewall
  • netfilter/iptables (This daemon provides firewall services. Those are not that necessary if you’re behind a router or smoothwall with a built-in firewall)
• InfraRed
  • irda (This daemon enables your computer to communicate with other devices using IR (InfraRed) hardware. If you haven’t got such hardware, you can safely disable this service)
  • lircd (This daemon provides remote control support using IR (InfraRed) receivers. Can be disabled if you don’t have hardware capable of receiving IR signals)
• Multiple CPU’s
  • irqbalance (This daemon balances interrupts over multiple CPU’s in the system. Can be disabled if you don’t have multiple CPU’s or a dual core processor)
• Software RAID
  • mdmonitor, mdadm and mdmpd (These daemons provide information about and management functionality over software RAID devices. They are unnecessary if you don’t use software RAID)
• DNS Server
  • named (also known as BIND) (This daemon provides DNS server functionality. It is usually not needed on workstations)
• Remote kernel logging
  • netdump, netcrashdump and netconsole (These services provide functionality for kernel logging and debugging over network connections. Only necessary if you want to view your kernel’s log and debugging messages on an other computer)
• Fileservers
  • NFS server
    • nfs (This daemon provides NFS server functionality, allowing other computers with NFS clients to connect to your computer and access files. You can disable this if you don’t need/want others to access your system using NFS)
    • portmap (This daemon manages RPC connections, used by protocols like NFS and NIS. Only needed on computers that need to act as a server)
    • rpcsvcgssd (This daemon manages RPCSEC GSS contexts for the NFSv4 server and is not needed unless you are running an NFS server)
  • Samba server
    • smbd and nmbd (These daemons provides other computers (Windows computers, too) with access to your files. This is not needed if you don’t want others to be able to access your files over the network)
• Network Authentication
  • nscd (This daemon handles passwd and group lookups and caches their results. Only needed when using a ‘slow’ name service, like NIS, NIS+, LDAP, or hesiod)
  • portmap (This daemon manages RPC connections, used by protocols like NFS and NIS. Only needed on computers that need to act as a server)
• Remote time setting
  • ntpd (This daemon sets your system time to a value it retrieves from a so-called ntp server, which usually serves a very accurate time. Although it is a useful feature, it tends to slow your system’s startup a lot, especially if the server cannot be found)
• Process Accounting
  • psacct (also known as acct) (This daemon provides process accounting, which gives a more detailed insight into the execution of commands on your system. This is usually not needed unless you are running a server that is accessed by a lot of people that you cannot trust entirely)
• Plaintext Authentication Requests
  • saslauthd (This daemon handles SASL Plaintext Authentication Requests, and is only required on a server that needs to communicate using SASL mechanisms)
• Mailserver
  • sendmail (This daemon sends and forwards email messages, acting as a server. You don’t need this daemon to be able to send a normal message. It is only needed if you need your computer to act as a mailserver)
  • spamd (also known as Spamassassin) (This daemon checks incoming mail messages for spam. This can usually be disabled, but keep in mind that some mail clients, like KMail, can use spamd’s functionality)
• SSH Server
  • sshd (This daemon allows remote login to your computer using the SSH protocol. It can be disabled if you don’t want/need this access)
• VNC Server
  • vncserver or xvnc (This daemon allows others to get a virtual graphical Desktop that actually runs on your computer)
• Task Scheduler
  • cron (and variants, like vixie-cron…) (This daemon runs periodic tasks on your system, like updating the search index or the manpage index, but also rotating logfiles. This one is generally required for a server system to run correctly, but workstations may be able to run without it)

Runlevels: 

• 0: Shuts down the system (to be switched to after booting)
• 1: Boots the system to a rescue mode
• 2: Boots the system to a multi-user mode without networking functionality (some systems, like Debian, use this as a full-fledged mode)
• 3: Boots the system to a multi-user mode with networking functionality (some systems, like Debian, use this as a full-fledged mode)
• 4: Generally not used (sometimes it is the same as runlevel 5 or 3)
• 5: Boots the system to a full-fledged graphical multi-user mode (with networking, of course)
• 6: Reboots the system (to be switched to after booting)
• (s or S: Usually similar or equal to runlevel 1)