iOS 4 features: Background app killing

iOS 4 background app kill

iOS 4's new fast app switcher interface also allows you to kill both Apple and 3rd party App Store apps that may be causing problems in the background.

To access the fast app switcher in iOS 4, double click the home button on iPhone 4 iPhone 3GS, or iPod touch G3. The interface will slide up and reveal a second dock-like set of app icons "in the background". To kill an app, tap and hold the app until the icons begin to jiggle, then tap the minus symbol (-) at the top left corner. The app will then disappear, "deleted" from the background dock (but not from your iPhone or iPod).

This force quiwill do a couple of different things depending on the type of app.

First, with built-in Apple apps, if you kill them from the fast app switcher, they will still keep running in the background. For example, if you kill Mail you will still receive Mail (it doesn’t kill the background thread that checks, sounds/vibrates, and updates the badge). Instead, it will force the background thread(s) to restart. If something isn't working right with Mail -- messages aren't showing up properly -- this is a great way to clean in out and get it going again. Likewise, it can force Safari to reload pages, iPod to fix weird behavior, and otherwise quickly handle problems that might not need a full reboot.

For App Store apps, if you kill them from the fast app switcher they will no longer function in the background. You'll still get push notifications because those are handled by an external server, but you'll lose things like background music playing, navigation, VoIP, and saved state (when you next launch the app, it won't be where you left it but will relaunch from the beginning). Again, if an app is misbehaving or otherwise giving you problems, killing it can be a quick way to force a refresh without having to resort to rebooting your iPhone or iPod touch.

Remember, you don't generally have to manage background apps in iOS 4. For apps that aren't streaming music, location (turn-by-turn navigation), or VoIP (like Skype) you only ever need kill them if they're obviously not working right. When it does come to streaming music, location, and VoIP, those can effect your battery life (especially background Skype right now), so you may want to keep a closer eye on them and kill them if you won't be using them for a while.

Note: for iOS 3.x, iPhone 3G, iPod touch G2, and earlier devices, you can kill all active background tasks by holding down the sleep button until the "slide to power off" screen appears, and then holding down the home button until you're reset to the home screen.

If you ever make use of the background app kill, let us know how it works for you. For more features, see our complete iOS 4 walkthrough.

Have something to say about this story? Leave a comment! Need help with something else? Ask in our forums!

Rene Ritchie

EiC of iMore, EP of Mobile Nations, Apple analyst, co-host of Debug, Iterate, Vector, Review, and MacBreak Weekly podcasts. Cook, grappler, photon wrangler. Follow him on Twitter and Google+.

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Reader comments

iOS 4 features: Background app killing


The background app kill helps me out with the problems with the Mail app. I have yahoo push mail, and sometimes when I get a new message, the alert will sound and the badge will update. However, when I enter the app, the message doesn't appear. After a kill in the multi-task menu though, the message appears when Mail is reopened.

Actually, in iOS 3.x and the 2nd gen iDevices, that method DOESN'T kill all background tasks, just the current one you're in.
Doing it from the springboard pretty much resprings the device.

I've had a few bugs with the mail app too, good thing it can be killed. still wish you could turn save state off completely for specific apps like the settings app, the only time I've ever wanted to go back to where I was in that app is when I'm messing around with wallpapers

I wish there was a way to close the kill function and keep the fast app switcher active. As it is now, I can kill some apps and then I have to go back to the springboard to find my app I want to use.

I've experienced a batery drain when GAMES are on the background.
Now i have to kill every 3rd party app on the hotapp switch.
Would be nice if apple just indicate a number of apps running on the background so i'd be a lot more easy to detect the cause of the problem.

The one that needs improving is a way to identify what state each app is in (ie. running, background active, background dormant, not running, etc...)

Shlavens says:
August 10, 2010 at 8:58 am
"Wishing there was a command to instantly close all open apps…"

On my 3GS I have to kill apps frequently. The worst episode was when the GPS stooped working until I killed almost everything in the background!
The multitasking needs to be much more robust.

I don't know if this is in any way related to the multi-tasking or not, but I've frequently noticed lately my ipod app (and everything else that plays sound) gets stuck. The volume doesn't change, regardless of what I set the volume to, and even flick the silent switch, and the music controls in the multi-task menu are all greyed out. Closing all active tasks, and then re-opening the ipod app fixes this, but it's still bizzare. Just closing the ipod app is not sufficient, however finding the specific app by trial and error does prevent having to close ALL active tasks, but it's not just one or two problem apps, it's random every time which app it is, with it even having been mail at one point.
closing every app is an annoyance surely, but much less of one than the reboot that would otherwise be required (though the iPhone 4 reboots obscenely fast, so even those are less of an annoyance than they used to be.)

Jobs: "If you see a stylus or a task manager, they blew it. "
Ironic the Android has advanced enough to make task managers unneeded and not recommended. Apple gives you quick access to its task manager and now its a feature.

August 10, 2010 at 9:04 am
Shlavens says: August 10, 2010 at 8:58 am “Wishing there was a command to instantly close all open apps…”

“Wishing there was a command to instantly close all open apps…”
Why, how many open apps do you have at any one time, I bet you don't even know the answer do you? What you think is "open" is just save stated, why would you want to close it when it's not even open?!
There's probably a max of 8 apps ever open, and that includes the inbuilt ones that you weren't able to close anyway.

In order to save space in my backgrounding dock, I will often "kill" apps that I know do not yet support the saved state feature. However, ever since the 4.0 and even now with the 4.0.1 update, the progress bar that appears at the bottom of the mail app has not been working. The rest of the app works fine but to prevent the progress bar from remaining on the screen 100% of the time, I have to do periodic kills of the app. That tends to be the main reason that I kill any app, however, I've had to use it on other apps when they've become buggy as well.

The problem is that your RAM is full, the two options to fix it are closing open apps, which you can do, or to upgrade your RAM, which you can do by buying the newest iDevice.
I often close background apps to free RAM so I can load more pages in safari without having to reload each page when I swipe back and forth.

"those can effect your battery life"
I'm no native English speaker, but wouldn't the correct word here be "affect"? I'm only asking because on this blog, I've seen this several times now and it's always bugged me a little bit.

Remember a while ago when people were saying how we all NEEDED TRUE multitasking like the super duper amazing Android?
Now we have limited backgrounding, and it's killing battery life, just not as fast...
I had an android device and I think Android sucks. It was getting so bogged down that I was missing calls because it was crashing when I was trying to answer the call.

This just proves to me that most of you guys haven't got a clue...
It doesn't effect (sic) battery life, they AREN'T even running (yes even the ones that don't support save states).
The only things that "could" be running are apps using one of the 7 background APIs Apple opened up to devs.
No apps pre iOS4 (unless rewritten to do this) will be running, all other apps that support save states will NOT be running, the're closed and their state is saved and restored, all apps that haven't been recompiled to support save states will NOT be running, they're closed and don't have a save state.
Do some research before spouting bullsh*t about what you "think" is happening...

Killing the app in the Fast App Switcher will also kill the saved state of the app.
You can see this by launching Plants vs Zombies, getting into a game, then switching out and back.
When you switch back to PvZ, the app is right where you left off, with a Pause Screen so you aren't thrown into the fight unfairly. This happens even if you switch between 4 or 5 apps, as well as launching it from the Home Screen.
Now, switch out of the app and "Kill" PvZ via the App Switcher. Relaunch it from the Home Screen. The game goes thru the whole startup process again (the rolling progress bar, etc).
@Mephisto: I am starting to move away from the side that thinks "it doesn't affect battery life because NOTHING is running", because from the looks of it, there ARE some things working in the background, or at the very least being held in ACTIVE memory (which uses up battery power to keep alive). I wonder if the "saved states" are actually being written to the 16-32GB Flash memory, or to the 512MB of RAM.

Accuweather's app is an example which you hace to quit completely as it does not refresh when sitting in the springboard.

On my 3GS I had to kill apps often to keep speed up, even free memory in SBS. on my I4 I can have alot more running, I don't find myself closing apps as often. Yes I know this is due to the increased memory.

Then Accuweather need to update their app to support refresh on resume (like eBay have just done).
RAM I assume as powering down the phone loses the save state too.
I recall some guy who had a jailbroken 3Gs running 4 and using one of the SYS tools you can get for it saying that when an app went into save state it no longer showed it as a running process.
It obviously usues up memory, and the bigger the footprint of the app the more memory it needs for it's save sate, hence why you can still lose a save state if the OS decides to "clear" it out if it's the least used and it needs the memory.
It won't be using any more battery life to hold a save state than it would without it, simply having the phone turned on uses as much!

I know that most backgrounded apps are not supposed to use any CPU, memory or battery, with the exception of active navigation, music streaming, and a couple other features. However, I have a sneaking suspicion that some do. For one thing, the performance of my 3GS is noticeably better with fewer frozen apps on the task bar. I have to make a habit of killing them. I have also proven that Slacker radio uses CPU and battery when backgrounded with the music paused. Pandora does not use CPU when paused. This is reproducible with the following:
1) Close all apps from the task bar and charge phone to 100% (this resets usage time to 0)
2) Remove phone from charger and do nothing for 1/2 hour
3) Check your usage statistics. It should say standby time 1/2 hour, usage time 0
4) Start Slacker, wait for a song to start, and then pause. Hit the home button to put Slacker in the background.
5) Do nothing for another 1/2 hour. Check your usage statistics. When I do this, I see standby time is 1 hour, usage time is 30 minutes.
If music was playing, I would expect the usage time to increase, but not when the music is paused. This proves to me that Slacker is using CPU and therefore battery even with the music paused.

RAM question as it pertains to backgrounding:
If apps running in the background are not using RAM, why does my available memory did so low (under 100MB) when I have a bunch of apps backgrounded? My peak RAM with no apps in background is about 350MB.
I'm curious what everyone else's RAM is like, with apps backgrounded and not.
(I use SBSettings on my iP4 to monitor memory usage).

What happens if one kills the phone app or the calender app? Also, is it possible to kill those and are there any benifits from it? Just wondering, thanks.

@Méphisto. I really hate flame wars but before insulting everyone you should be a bit more careful than that. Some apps ARE running in the background. Yes, THEY ARE (since you like capitals)
In two hours my battery can go from 100% to 50%.
I haven't identified the offending app(s) yet but fact is that killing everything stops the drain.
There. And do some research yourself. And for the record, we've been able to kill native apps since os 1.0. Ever heard of holding the home button?

August 10, 2010 at 9:04 am Shlavens says: August 10, 2010 at 8:58 am “Wishing there was a command to instantly close all open apps…”
+1 gazillion.
Sometimes I'll have 15 apps open at one time and its a little pain closing them one by one. I'd much rather have a command where I can kill everything, either via apple or the JB world.

Feel free to back up your assumptions with facts, and while your at it feel free to explain what holding the home button does as I don't believe you actually know...

Holding the home button did (and still does on iPhone 2G) kill the currently running app. Then, VoiveOver was introduced and you had to hold the power button, then the home button to accomplish that task. Does that answer your question?
I was in fact trying to enlighten people on your "and that includes the inbuilt ones that you weren’t able to close anyway" that you mentioned earlier. Anyone can and always could close apps, inbuilt or not.
Other than that what assumption do you want me to backup? The fact that some apps can run on the background? Please watch the latest keynote available as a poscast or on Apple's website. AFAIK, that was the only assumption I was making.

Apologies about the home button, I wasn't aware of that, only way I knew of killing inbuilt apps was via SBSettings when I had my phone jailbroken.
As for running in the background, I did state that apps which had been built to use one of the 7 APIs as released by Apple would run in the background (and as someone has pointed out, pausing some apps doesn't stop them "running"), however all other apps will either save state and close, or just close, using up RAM but not battery life.
Unless you're going to tell me that sitting in RAM uses battery...

@Tom. On the Slacker question - you pressed pause. It will pause and continue to buffer so it will resume from where it left off on pressing play again. Therefore it is still running, using a lot of data too! Does slacker not have a stop button? Thats what you should press to stop it.
Tunein Radio has a pause or a stop button. You can set it up so the pause button also acts as a stop button so its stops buffering and no process continues to run. Works exactly as I want it to and I don't have to close it
I only ever close an app from the fast app switcher if its gone 'funny'. Otherwise I leave all apps in there and I haven't noticed any battery life or performance issues.
Oh and I think Accuweather has now been updated so it refreshes on relaunch

Aldo - Thanks. No, Slacker does not have a stop button. I do not have Slacker caching turned on. The same test with Pandora shows no usage at all. Why would it be different?
When playing in the background, there is a little play icon near the battery icon. When it is paused, this is not there. I would hope that if Slacker were still downloading and buffering music, this icon would still be present. I guess not.

You said "This just proves to me that most of you guys haven’t got a clue…" when people complained that some apps ate their battery life. Care to give us the clue? Because some poorly thought out apps just do that. That's life out there today, not a dream.

What am I missing: when I quit the MapQuest app — when I've arrived at my destination — it sure seems like it is still going in background, “updating my location” as I walk into a building, etc. That seems to take a slug of CPU.
Yeah, I can go to the the gallery of recently run apps and torch it from there, but this seems ugly.
Did Apple not provide apps a way to actually quit when their services are no longer needed? Have I missed seeing it on this free app?

@Walt French: Apps don't need a way to terminate. It's up to the developer to decide when their app is done. GPS apps have a way of staying in the background and if the dev didn't provide a way to end it, it is stuck there...

I use it when I need to force kill an app for some reason, mostly because apps not quite working right on iOS4. I'm also kinda OCD about letting things run that aren't being used, so for apps that I hardly use, I usually kill it right when I'm done. For apps I occasionally use, I kill them if I'm already killing another app, but I usually don't bother with apps I use all the time. Apps don't need to be taking up extra resources for no real reason (no matter how few amount of resources it may be).

I'm specifically talking about those people in this thread that come out with comments like "give us a close all option", like they think everything they have in their fast switch dock is still running, well that's just not true.
As for these poorly thought out apps, I'm still waiting for you to name one of them.

Well, given that there is no control panel of any sort on the iPhone, how can one identify which of the 20+ apps in the fast switch dock is running and is poorly written? Heck, how to know which one consumes some CPU or some network bandwidth? Or which one uses the GPS? There is no way.
This is why a "close all" option makes sense, because it closes everything and you can be sure that the offending app is closed as well. Not perfect by any means, but it would get the job done. Because when I see my battery go down, I generally don't have time to nitpick and guess at which app does it.
Now, through trial and error I may be able to detect which one of my apps is eating up my battery, and givn enough time I will. But that's a bit hard, you'll have to admit that.
I've been told that Android has a control panel where it estimates the battery consuption of all apps. THAT would be great to spot the offenders quickly. Short of that...

What is the limit for apps in the fast switch dock? I just closed 96 apps. Pretty useless to have it go that high.

Men I am so HAPPY that I found this tip !!!!
I've been fighting with skype for dayssss
It would not stop working in the background and everything my friends were typing for me, or myself typing on my computer would SHOW up on my iphone screen :-(
I was ging nuts
THANKS a lot for the post

Actually there's a problem with killing apps in VoiceOver. In VoiceOver, the iPhone talks you thru the various features. When you eventually manage to get to the MultiTasker, there's no obvious way to get to the KILL feature. Anyone know how to do this? I've got a blind friend that has no way to stop apps from running other than to completely shut down the iPhone and restart it.

You can find clearly some bunch towards identify concerning this. My spouse and i feel you have made various decent points in characteristics furthermore.

Killing apps once you are done with them.. is it a efficient way to conserve battery ? or I don't have to care about killing apps unless I have issue with the app.

Killing apps once you are done with them.. is it a efficient way to conserve battery ? or I don't have to care about killing apps unless I have issue with the app.

You forgot to mention a very important and EXPENSIVE result of leaving the apps running. When you're not using WIFI, they are still running on the 3G network and using data. I've gone over my allotted MB usage several times without getting any benefit from the apps. I was puzzled by my phone using more data even when I had cut almost all conscious use. A $15 pop several months in a row lead me to discovering this data sucking feature of running these apps in the BG.

You really make it appear really easy together with your presentation however I find this topic to be actually one thing that I believe I'd never understand. It seems too complex and very large for me. I'm having a look forward in your subsequent post, I'll try to get the dangle of it!