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Linux commands, scripts, examples, tutorial

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Linux. Services, description, purpose

 
NetworkManager, NetworkManagerDispatcher
NetworkManager is daemon meant to automate switching between network connections. Many laptop users who switch between Wireless WiFi connections and Ethernet connections may find this useful. Most stationary computers should have this disabled. Some DHCP users may require this.

acpid
Advanced Configuration and Power Interface daemon which controls and allows interfacing to power management and certain input devices. It is recommended to be enabled for all laptops, and most desktops. Some servers may not require acpi. Common things supported are the "Power Switch", "Battery Monitor", "Laptop Lid Switch", "Laptop Display Brightness", "Hibernate", "Suspend", etc.

anacron, atd, cron
These are schedulers with each having slightly different purposes. It is recommended you keep the general purpose scheduler cron enabled, especially if you keep your computer running for long periods of time. If you are running a server look into which schedulers you require. Most likely atd and anacron should be disabled for desktops/laptops. Please note that some sheduled tasks such as cleaning /tmp or /var may require anacron.

apmd
Is used by some laptops and older hardware. If your computer supports acpi, then apmd should probably be disabled.

auditd
This saves audit records generated by the kernel. Not entirely sure how this information is used, however it is useful for diagnosing issues with SELinux. For now I have this enabled. This is optional, however it may useful for servers or machines with multiple users and highly recommended for SELinux users.

autofs
This mounts removable disks (such as USB harddrives) on demand. It is recommended to keep this enabled if you use removable media.

avahi-daemon, avahi-dnsconfd
Avahi is an implementation of zeroconf and is useful for detecting devices and services on local network without a DNS server. This is also the same as mDNS. Most likely this is unnecessary unless you have compatible devices/services. I have this disabled.

bluetooth, hcid, hidd, sdpd
Bluetooth is for portable local wireless devices (NOT wifi,802.11). Some laptops come with bluetooth support. There are bluetooth mice, headsets and cell phone accessories. Most people do not have bluetooth support or devices, and should disable this. Other services with bluetooth: hcid manages all devices, hidd provides support for input devices (keyboard, mouse).

cpuspeed
This throttles your CPU runtime frequency to save power. Many modern laptop CPU's support this feature and now some desktops also support this. Most people should enable only if they are users of Pentium-M, Centrino, AMD PowerNow, Transmetta, Intel SpeedStep, Athlon-64 hardware.


cupsd, cups-config-daemon
Used for printing. These should be enabled only if you have CUPS compatible printer that works in Fedora.

dc_client, dc_server
Distcache is for distributed session caching. It is primarily for SSL/TLS servers. Apache can use this. Most desktop users should have these disabled.

dhcdbd
This basically an interface for the DBUS system to control DHCP on your computer. It can be left to the default disabled state.

diskdump, netdump
Diskdump is a mechanism to help debug kernel crashes. It save a "dump" which can be later analyzed. Netdump does something similar over the network. Unless you are diagnosing a problem, these should be left as disabled.

firstboot
This service is specific to Fedora's installation process meant to perform certain tasks that should only be executed once upon booting after installation. Even though it verifies it has been run before, it can be disabled.

gpm
This is the console mouse pointer (no graphics). If you do not use the text console (CTRL-ALT-F1,F2..) then disable this. However I leave this enabled for runlevel 3 and disabled for runlevel 5.

hidd
See bluetooth.

hplip, hpiod, hpssd
HPLIP is a service to support HP printers in Linux, including Inkjet, DeskJet, OfficeJet, Photosmart, Business Inkjet and some LaserJet printers. This supported by HP through HP Linux Printing Project. HPLIP should be enabled only if you have a supported compatible printer.

iptables
This is the standard Linux software firewall. This is required if you are directly connected to internet (cable, DSL, T1). It is not required if you use a hardware firewall (D-Link, Netgear, Linksys, etc) but it is highly recommended.

irqbalance
This service is to increase performance across processors on a multiprocessor system. Since most people do not have multiple processors, it should be disabled. However I do not know how it affects multi-core CPU's or hyperthreaded CPU's (?). There should be no problems on single CPU systems that do not use this.

isdn
This is another form of internet connect service/hardware. Unless you have an ISDN modem, disable this.

kudzu
This runs the hardware probe, and optionally configures changed hardware. If you swap hardware or need to detect/re-detect hardware this can be left enabled. However most desktop or servers can disable this and run it only when necessary.

lm_sensors
This monitors motherboard sensor values or specific hardware (commonly used with laptops). It is useful for watching realtime values for PC health, etc. This is also popular with GKrellM users. More information on lm_sensors homepage. It is recommended to disable this unless you have a need.

mdmonitor
Is useful for monitoring Software RAID or LVM information. It is not a critical service and be disabled.

messagebus
This is an IPC (Interprocess Communication) service for Linux. Specifically this communicates with dbus, a critical component. It is highly recommended to leave this enabled.

netdump
See diskdump.

netplugd
Netplugd can monitor network interfaces and executes commands when their state changes. This can be left to default disabled.

netfs
This is used for automatic mounting of any shared network file space such as NFS, Samba, etc on bootup. Useful if you connect to another server or filesharing on your local network. Most single desktop/laptop users should have this disabled.

nfs, nfslock
This the standard network file sharing for Unix/Linux/BSD style operating systems. Unless you require to share data in this manner, disable this.

ntpd
This automatically updates the system time from the internet. Mentioned in the installation process. If you have an active ("always-on") internet connection it is recommended you enable this, but it is not required.

portmap
This is complementary service to NFS (file sharing) and/or NIS (authentication). Unless you use those services you should disable this.

readahead, readahead_early
This services is to improve startup performance by preloading certain applications into memory. If you wish to startup faster leave this enabled.

rpcgssd, rpcidmapd, rpcsvcgssd
Used for NFS v4. Unless you require or use NFS v4, these should be disabled.

sendmail
Unless you run a server or you like to transfer or support a locally shared IMAP or POP3 service, most people do NOT need a mail transport agent. If you check your mail on the web (hotmail/yahoo/gmail) or you use a mail program such as Thunderbird, Kmail, Evolution, etc. then you should disable this.

smartd
The SMART Disk Monitoring Daemon can be used to monitor and predict disk failure or problems on hard disk that support this. Most desktop users may not need this unless there is possible problems, but is it recommend to be left enabled (especially for servers).

smb
The SAMBA daemon is required to share files from Linux to Windows. This should be enabled only if you have windows computers that require file access to Linux. There is information on configuring Samba for FC5.

sshd
SSH allows other users to log into or run applications on your computer from another computer on your network or remotely. This is a potential security issue. This is not needed if you have no other computers or no need to login from a remote location (work, school, etc.). Most likely this should be disabled.

xinetd
This is a special service. It can launch multiple services based on a request to a specific port. For example: telnet is typically connected to port 23. If there is a request for telnet access that xinetd detects on port 23, then only will the telnet daemon be executed. For convenience this can be left to enabled. Run system-config-services and go to On Demand Services -or- run chkconfig --list and look for the xinetd output to show which services are connected to 
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