Understanding various system services in Linux

Any released version of linux has the following system services. This article describes these services one by one. It is recommended that you take some time to understand the functions of these services, so that you can clearly know which services you should use. NetworkManager, NetworkManagerDispatcher...

Any released version of linux has the following system services. This article describes these services one by one. It is recommended that you take some time to understand the functions of these services, so that you can clearly know which services you should use.
NetworkManager, NetworkManagerDispatcher
NetworkManager is a background service program built on HAL and provides a more focused network management function. Including network interface management and network status query, and supports general network, dial-up network, and wireless network. many notebook users need to enable this function, it allows you to switch between a wireless network and a wired network. Most desktop users should disable the service. Additionally, additional functions such as VPN, DHCP, and DNS are provided.

Acpid
The ACPI (Advanced Configuration and Power Interface) service is a Power management Interface. We recommend that you enable it for all notebook users. Some servers may not need acpi. Common operations supported include: "Power Switch", "battery monitoring", "notebook Lid switch", "laptop display brightness", "sleep", "Hanging Up", and so on.

Anacron, atd, crond
There is a small difference between these scheduling programs. We recommend that you enable cron. if your computer runs for a long time, you should enable it. For servers, you should have a better understanding of which scheduler should be enabled. In most cases, atd and anacron should be disabled for laptops/desktops. Note: anacron is required for executing some tasks, such as cleaning/tmp or/var.

Alsasound
Alsa audio card driver daemon. The Alsa sound card driver was originally written for a sound card Gravis UltraSound (GUS). The program was proven to be excellent, so the author began to write drivers for a general sound card. Alsa is compatible with OSS/Free and OSS/Linux, but it has its own access port, which is even better than OSS.

Apmd
Some laptops and old hardware use apmd. If your computer supports acpi, you should disable apmd. If acpi is supported, the work of apmd will be completed by acpi.

Arptables_jf
Controls the daemon for users in the arptables network.

Arpwatch
Record logs and build an Ethernet address and IP address pair database that is visible on the LAN interface.

Atalk
AppleTalk network daemon. Do not run the program in the background. The data structure of the program must be initialized for a certain period of time before other processes are run.

Auditd
The audit subsystem can be used by the system administrator to monitor system calls and access to those file systems that comply with the audit requirements or other audit requirements. Its main contents include:

By default, audit is disabled in the kernel. However, when the auditd software is installed, running the software will start the audit Daemon (auditd ).
When auditd is running, the audit information is sent to a user configuration log file (the default file is/var/log/audit. log ). If auditd is not running, the audit information will be sent to syslog. By default, the information is put into/var/log/messages. If the audit subsystem is not enabled, no audit information will be generated.
These audit information includes SELinux AVC information. In the past, AVC information was sent to syslog, but now the audit daemon is sent to the audit log file.
To disable audit completely in the kernel, use the audit = 0 parameter at startup. You also need to use chkconfig auditd off 2345 to disable auditd. You can use auditctl-e 0 at runtime to disable audit in the kernel.
The audit Daemon (auditd) obtains audit event data from the kernel's audit netlink interface. The configuration of auditd varies. for example, you can configure parameters of the output file and log file disk in the/etc/auditd. conf file. Note that if you set up your system to audit the CAPP style, you must set a dedicated disk partition for use only by the audit daemon. This partition should be mounted to/var/log/audit.

The system administrator can also use the auditctl tool to modify audit parameters, syscall rules, and view file systems when the auditd daemon is running. It contains a sample of the CAPP configuration. you can copy it to/etc/audit. rules to make it work. You can use the ausearch tool to view and search audit log data.

Autofs
This service automatically mounts removable storage (such as a USB hard disk ). If you use mobile media (such as mobile hard disks and USB disks), we recommend that you enable this service.

Avahi-daemon, avahi-dnsconfd
Avahi is the implementation of zeroconf protocol. It can discover zeroconf-based devices and services in a LAN without DNS services. It is the same as mDNS. Disable it unless you have compatible devices or services that use the zeroconf protocol.

Bootparamd
Bootstrap parameter server, which provides information required for bootstrap for diskless workstations on the LAN.

Bluetooth, hcid, hidd, sdpd, dund, pand
Bluetooth is used for wireless portable devices (non-wifi, 802.11 ). Many laptops provide Bluetooth support. There are Bluetooth mouse, Bluetooth headset, and mobile phones that support Bluetooth. Many people do not have Bluetooth devices or services related to Bluetooth, so they should be disabled. Other Bluetooth-related services include: hcid to manage all visible Bluetooth devices, hidd to provide support for input devices (keyboard, mouse), and dund to connect to the network through Bluetooth dialing, pand allows you to connect to Ethernet via Bluetooth.

Capi
It is only useful for users who use ISDN devices. Most users should close it.

Chargen
Chargen server (Character Generator Protocol), which uses the tcp Protocol, is a network service. its main function is to provide functions similar to remote typing.

Chargen-udp
Use the chargen server of UDP protocol.

Chargen-dgram
Chargen-stream

Conman

Cpuspeed
This service can dynamically adjust the CPU frequency during operation to save energy (power ). Many laptops support this feature, and more desktops now support this feature. If your CPU is: pew.m, Centrino, AMD PowerNow, Transmetta, Intel SpeedStep, Athlon-64, Athlon-X2, one of Intel Core 2, you should turn it on. If you want your CPU to run at a fixed frequency, disable it.

Cupsd, cups-config-daemon, cups-lpd
Printer problems.

Cvs
Cvs is a version control system.

Daytime
The Daytime daemon of TCP is used to obtain the date and time from the remote server for the client. Default Port: 13.
Daytime-udp
Use the Daytime daemon of UDP.

Daytime-dgram
Daytime-stream

Dc_client, dc_server
The disk cache (Distcache) is used for distributed session cache. It is mainly used for SSL/TLS servers. It can be used by Apache. Most desktops should close it.

Dhcdbd
This is an interface for the guest system to control DHCP. The default off status can be retained.

Diskdump, netdump
Diskdump is used to help debug kernel crashes. After the kernel crashes, it will save a "dump" file for analysis. The Netdump function is similar to Diskdump, but it can be stored over the network. Unless you are diagnosing kernel-related issues, they should be disabled.

Discard-dgram
Discard-stream

Dnsmasq
DNSmasq is a lightweight and easy-to-use DNS service tool. it can be used for NAT translation of IP addresses during intranet and Internet connections, or as a DNS service for small networks.

Echo-udp
The server that uses the UDP protocol returns the client data service daemon.
Echo-dgram
Echo-stream

Eklogin
A service daemon that accepts rlogin session authentication and encrypts it with kerberos5.

Ekrb5-telnet

Firstboot
This service is unique to the installation process of Fedora. It only needs to execute a specific task once when it is started for the first time after installation. It can be disabled.

Functions

Gated
Gateway Routing Daemon. It supports various routing protocols, including RIP version 1 and 2, dcn hello protocol, OSPF Version 2, and EGP version 2 to 4.

Gpm
Terminal mouse pointer support (no graphical interface ). If you do not use a text terminal (CTRL-ALT-F1, F2..), close it. However, I enable it at runtime level 3 and disable it at runtime level 5.

Gssftp
Use the ftp daemon for kerberos 5 authentication.

Haldaemon
Halt

Maid, hpiod, hpssd
HP printer support is available in Linux, including Inkjet, DeskJet, OfficeJet, Photosmart, Business InkJet, and some LaserJet printers. This is the product of HP Linux Printing Project sponsored by HP. If you have a compatible printer, enable it.

Hsqldb
A java Relational Database Daemon is named after Hypersonic SQL, but this project has not continued.

Httpd
The Apache daemon of the Web server can be used to provide HTML files and CGI dynamic content services.

Innd
Usenet news server daemon.

Iiim
The daemon process of the Chinese input method server.

Inetd
Internet operation daemon. The monitoring network needs various services managed by it, and starts corresponding service programs when necessary. It is replaced by xinetd in Redhat and Mandrake linux. Debian, Slackware, and SuSE are still used.

Ip6tables
If you do not know whether you are using IPv6, it is generally not used. This service is a software firewall for IPv6. Most users should close it.

Ipmi
Iptables
It is a Linux standard firewall (software firewall ). If you directly connect to the Internet (such as cable, DSL, T1), we recommend that you enable it. If you use a hardware firewall (such as D-Link, Netgear, and Linksys), you can disable it. We strongly recommend that you enable it.

Irda, irattach
IrDA provides communication support between infrared devices (laptops, PDA's, mobile phones, calculators, and so on. Most users should close it.

Irqbalance
In a multi-processor system, enabling this service improves system performance. Most people do not use a multi-processor system, so disable it. But I don't know how it works on the multi-core CPU's or hyper-threading CPU's system. Disabling it in a single CPU system should not cause problems.

Isdn
This is an Internet access method. Unless you use ISDN cat to access the Internet, you should disable it.

Keytable
The function of this process is reprinted in the keyboard ing table defined in/etc/sysconfig/keyboards. This table can be selected using the kbdconfig tool. You should make the program active.

Kdump

Klogin
Log on to the daemon remotely.

Krb5-telnet
Use the telnet daemon for kerberos 5 authentication.

Kshell
Kshell daemon.

Killall
Krb524
Kudzu
This service performs hardware detection and configuration. If you change the hardware or need to detect hardware changes, enable it. However, most desktops and servers can be shut down and started only when needed.

Ldap
Ldap (Lightweight Directory Access Protocol) Directory Access Protocol server daemon process.

Libmongod

Lm_sensors
This service can detect the value of the sensor device on the motherboard or the status of specific hardware (usually used in laptops ). You can use it to view the real-time status of your computer and understand its health status. It is popular among GKrellM users. We recommend that you disable it for no special reason.

Lvm2-monitor
Mcstrans
SELinux conversion service. if you use SELinux, enable it, but you can also disable it.

Mdmonitor
This service is used to monitor Software RAID or LVM information. It is not a critical service. you can disable it.

Mdmpd
This service is used to monitor Multi-Path devices (this type of storage devices can be accessed by more than one controller or method ). It should be disabled.

Messagebus
This is the Linux IPC (Interprocess Communication) service. Specifically, it interacts with tranquility and is an important system service. We strongly recommend that you enable it.

Multipathd, microcode_ctl
It can encode and send new microcodes to the kernel to update the Intel IA32 series processor daemon.

Mysqld
A fast, efficient, and reliable lightweight SQL database engine daemon process.

Named
DNS (BIND) server daemon.

Netconsole

Netfs
This service is used to automatically mount shared file spaces in the network when the system starts, such as NFS and Samba. If you connect to another server in the Lan and share files, enable it. Most desktop and notebook users should disable it.

Netplugd, ifplugd
Netplugd is used to monitor network interfaces and execute specified commands when the interface status changes. We recommend that you keep the default off status.

Network
Activate/disable network interface Daemon at startup.

Nfs, nfslock
This is a standard file sharing method for Unix/Linux/BSD operating systems. Disable it unless you want to share data in this way.

Nscd
Service name cache process, which provides faster verification for services such as NIS and LDAP. if you run these services, you should enable them.

Ntpd
The service automatically updates the system time over the Internet. If you can maintain a permanent internet connection, we recommend that you enable it, but it is not necessary.

Pcscd
The service supports smart cards (the same size as small chips embedded in credit cards and identification cards) and smart card readers. If you do not have a card reader device, disable it.

Pcmcia
It is mainly used to support the laptop interface daemon process.

Portmap
This service is complementary to NFS (file sharing) and NIS (verification. Disable NFS or NIS unless you use the NFS or NIS service.

Postgresql
PostgreSQL relational database engine.

Pppoe
ADSL connection daemon.

Proftpd
Proftpd is a Unix-based ftp server daemon with flexible configuration.

Psacct
The daemon includes several tools used to monitor process activity, including ac, lastcomm, accton, and sa.

Random
The high-quality random number generator for saving and restoring the system. these random numbers are provided by some random behaviors of the system.

Rawdevices
The daemon used to load raw devices when using the cluster file system.

Rdisc
Readahead_early, readahead_later
This service provides performance by pre-loading specific applications to the memory. If you want the program to start faster, enable it.

Restorecond
Used to monitor SELinux and reload the correct file context (file contexts ). It is not necessary, but it is strongly recommended to enable it if you use SELinux.

Rhnsd
Red Hat Network service daemon. Notify the official security information and patch the system.

Routed
The daemon supports automatic IP route table maintenance for the RIP protocol. RIP is mainly used on small networks. a larger network requires a more complex protocol.

Rpcgssd, rpcidmapd, rpcsvcgssd
Used for NFS v4. Disable NFS v4 unless you need it or use it.

Rsync
Remote sync remote data backup daemon.

Rsh
Start a shell on the remote host and execute user commands.

Rwhod
Allows remote users to obtain a list of all logged-on users on the machines running the rwho daemon.

Rstatd
A waiting process for other machines on the LAN to collect and provide system information.

Ruserd
Remote User location service, an RPC-based service that provides user information about a machine log recorded on the LAN.

Rwalld
Activate the rpc. rwall service process, which is an RPC-based service that allows users to write messages to other terminals registered on the LAN machine.

Rwhod
Activate the rwhod service process, which supports the rwho and ruptime services of the LAN.

Saslauthd
Use the SASL authentication daemon.

Sendmail
Unless you manage an email server or want to transmit or support a shared IMAP or POP3 service in the LAN. Most people do not need an email transmission proxy. If you send and receive emails through a webpage (hotmail/yahoo/gmail) or using a mail sending and receiving program (such as Thunderbird, Kmail, Evolution, etc. You should close it.

Setroubleshoot
Program for viewing selinux logs

Squid
The squid daemon of the proxy server.

Smartd
The SMART Disk Monitoring service is used to monitor and predict Disk failures or Disk problems (prerequisite: the Disk must support SMART ). Most desktop users do not need this service, but we recommend that you enable it, especially for servers.

Smb
The SAMBA service is required for file sharing between Linux and Windows. If a Windows user needs to access a file on Linux, enable it.

Snmpd
The local Simple Network Management daemon.

Sshd
SSH allows other users to log on to your system and execute programs. the user can be a network or remote user. Enabling It has potential security risks. If you do not need to log on from another machine or remotely, disable it.

Syslog
Tcpmux-server
Tftp

Time
The daemon obtains the time and date from the remote host using the TCP protocol.

Time-udp
The daemon obtains the time and date from the remote host and uses UDP protocol.
Time-dgram
Time-stream

Tux
Run the Daemon of the apache server in the Linux kernel.

Vsftpd
Vsftpd server daemon

Vmware-tools
Vmware-tools, which is only available after the vmware-tools package is installed in the virtual machine.

Vncserver
VNC (Virtual Network Computing) provides a lightweight protocol for displaying the entire desktop of a remote computer on a local system.

Winbind
Winbind is a Samba component. in CentOS, it is included in the samba-common package. Winbind implements Microsoft's RPC call, plug-in verification module, and name service switch on Linux. it can contact Windows domain control through the samba interface, allows NT Domain users to operate as Linux users on a Linux host. By setting nss configuration for Linux server, we can let the system parse user information through the Winbind program.

Wpa_supplicant
Wireless network interface service

Xend, xendomains
XEN virtual services

Xfs
X Window Server Daemon provides a font set for local and remote X servers.

Xinetd
(This service may not be installed by default) it is a special service. It can start multiple services according to the requests received by a specific port. For example, a typical telnet program connects to port 23. If a telent request is detected by xinetd on port 23, xinetd starts the telnetd service to respond to the request. You can enable it for ease of use. Run chkconfig Clist and check the output related to xinetd to find out which services are managed by xinetd.

Ypbind
Activate the ypbind service process for the NIS (network information system) client.

Yppasswdd
The NIS password server daemon.

Ypserv
The NIS master server daemon.

Yum, yum-updatesd
The RPM operating system automatically upgrades and software package management daemon.

Author: flying bicycles"