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accessoryd
If removed, disables accessories like FM radio transmitters, iPhone docks, and AV cables. Accessories will be able to charge your device, but that is all they will be able to do.
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AddressBook
If removed, Contacts in the Phone application will load slightly slower.
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AdminLite
This daemon tries to return control of your device to you if it thinks that you are waiting for a lengthly process to respond. It does this by force-quitting the process.
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aggregated
It is performs some function related to Audio-In.
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AOSNotification
This daemon deals with MobileMe syncing.
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AppStore
Apple's "AppStore" application.
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apsd
Logs push notification errors. If removed, Push Notifications will no longer work.
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awd_ice2
Apparently only affects the iPhone 3G and 3GS. It's not known what its function is on those devices.
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awd_ice3
Only affects the iPhone 4. It's not known what its function is on the iPhone 4.
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BTServer
If this daemon is disabled, your device will become extremely slow and unresponsive.
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chum
This daemon is thought to relate to Apple's CHUD (Computer Hardware Understanding Developer) tools.
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CommCenter
Deals with making and receiving phone calls and connecting to the cellular data network.
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configd+pm
Deals with system configuration.
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configd-pm
Also deals with system configuration.
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Cydia
It's believed that this daemon deals with the AutoInstall trick for installing .deb files.
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daily
Nothing is currently known about this daemon, except that it is programmed to perform a certain function once a day.
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dataaccessd
If removed, contacts will no longer sync via Exchange or Google Sync.
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datamigrator
Used to transfer contacts from SIM card to phone.
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debugserver
Used by developers for debugging iOS applications on device. .
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dynamic_pager
This is what drives virtual memory (VM) mods.
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fairplayd
This checks the DRM on your legitimately-acquired music and apps.
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food
Installed by Comex's Frash plugin. This daemon most likely allows the interpretation of Flash content on webpages.
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gmmd
A debugging service for your device.
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graphicsservices
Thought to have something to do with displaying album artwork.
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iapd
Functions like com.apple.accessoryd. It deals with accessories that also come with companion apps.
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itdbprep
This has something to do with syncing music to your device.
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itunesstored
Messing with this daemon will cause it to use 100% of your device's CPU periodically. Leave it alone.
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insomnia
Used to keep Insomnia running through resprings and reboots.
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installd
Deals with app installation.
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iqagent
This daemon's function is currently unknown.
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Kernel task
It is the basic virtual memory manager.
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Launch daemon
Launchd is a unified, open source service management framework for starting, stopping and managing daemons, applications, processes, and scripts.
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locationd
Deals with GPS and location.
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Lockbot
This daemon's function is device's lock.
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Lockdown
Deals with SIM and network authorization. iPod touch users, even though this daemon seems like it deals with iPhone-only operations, have still had to restore after deleting this daemon.
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mDNSResponder
DNS. Disable this, and your Internet is completely gone.
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mDNSResponderHelper
Also deals with DNS.
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mDNSResponderHelper
Also deals with DNS.
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Media remoted
Allows the music buttons to be used to control 3rd Party apps(I.e. Pandora).
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mediaserverd
Plays your music and videos.
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MobileInternetSharing
Used for Internet Tethering.
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mtmergeprops
Important part of touchscreen service.
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MxT2d
The daemon that allows MxTube to download videos in the background. If disabled, the application will need to be reinstalled.
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notifyd
Server for the iOS notification system.
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notification_pro
Part of iOS notification system. Responsible for push notifications.
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obliteration
This daemon wipes the data partition of your device. This will be used if you remotely wipe your phone via Exchange, or if you use Settings > General > Reset, or if you set your device to wipe itself after a certain number of failed passcode entries.
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pasteboardd
This daemon deals with copy/paste.
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pilotfish
This daemon is also thought to relate to Apple's CHUD tools.
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powerlog
This is used to monitor any incompatibilities with 3rd party chargers.
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ptpd
Used to create VPN connections.
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pppd
Point-to-Point Protocol daemon which is used to manage network connections between two nodes. The role of pppd is managing PPP session establishment and session termination.
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profile_janitor
This daemon apparently deals with provisioning profiles for ad-hoc app distribution. If that doesn't apply to you, or if you have no idea what that is, you can delete this daemon.
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psctl
No definitive information about this daemon is currently available, but it's believed that it deals with connecting external storage devices, possibly a feature coming in new iDevices.
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racoon
Used for Virtual Private Networks.
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sbsettingsd
Related to SBSettings.
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SCHelper-embedded
Appears to be a part of the SystemConfiguration framework, so I don't recommend deleting it. If some brave soul wants to try it, go ahead and report back.
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scrobbled
The Scrobbler daemon.
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scrod
This daemon deals with Voice Control.
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searchd
Disables Spotlight search if removed. The Spotlight page will still be there, but nothing will show up when you start typing.
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SpringBoard
This daemon ensures that SpringBoard launches when you turn your device on. Without this daemon, SpringBoard will not launch. Also, this daemon ensures that you are able to respring your device.
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stackshot
This daemon's function is currently unknown, but removing it has no adverse effects on device.
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storage_mounter
This daemon's function is currently unknown, but it is believed that it deals with a possibly upcoming iOS feature that will allow you to use your iPhone or iPod touch in disk mode.
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SuperCharged
The SuperCharged daemon, which is a virtual memory mod from Cydia.
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syslogd
Logs system events.
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usbptpd
Allows your device to connect to your computer and charge.
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voiced
Yet another Voice Control daemon.
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VoiceOverTouch
Another Voice Control daemon.