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| EBC3 | morning all | 14:49 |
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| the_hydra | i am ready for the upcoming session... | 15:49 |
| resno | 6 more mins | 15:54 |
| nigelb | Folks, special announcement. | 15:58 |
| nigelb | Today is the_hydra's birthday! | 15:58 |
| nigelb | And he's celebrating that by giving a session in -classroom! | 15:58 |
| * the_hydra bows to everyone | 15:58 | |
| resno | happy birthday the_hydra | 15:59 |
| resno | by the way, we arent muted ;) | 15:59 |
| the_hydra | resno: thanks...I hope I do something meaningful | 15:59 |
| the_hydra | ok, is it now? | 15:59 |
| resno | the_hydra: me too | 15:59 |
| resno | its 11 am! | 16:00 |
| the_hydra | ok, let's begin, shall we? | 16:00 |
| nigelb | hang on for a minute | 16:01 |
| the_hydra | k... | 16:01 |
| nigelb | the classbot should kick in | 16:01 |
| resno | whats the chat channel? | 16:02 |
| the_hydra | "ubuntu-classroom-chat" AFAIK | 16:03 |
| resno | thanks | 16:03 |
| the_hydra | ok people, let's roll | 16:03 |
| the_hydra | today, I am gonna discuss about how to use monitoring tools in Linux to pinpoint system problems such as lack of RAM and so on | 16:03 |
| the_hydra | what we're gonna quickly observe here is top, vmstat and friends | 16:04 |
| the_hydra | "top" is a classic...you will likely find it in every UNIX flavour.... | 16:04 |
| the_hydra | if you look closer, "top" display almost everything, your CPU usage, memory usage, process statistics | 16:05 |
| the_hydra | they're either displayed as percentage or number...mostly.. | 16:05 |
| the_hydra | for example, CPU usage...are divided into user and system (marked as "us" and "sy") | 16:06 |
| the_hydra | anyone has idea what they mean? | 16:06 |
| c2tarun | us: processes that are controlled by user account | 16:07 |
| c2tarun | and don't have there system account (i guess) | 16:07 |
| the_hydra | other ideas? | 16:07 |
| obengdako | well like you said us for user and sy for system | 16:07 |
| the_hydra | alright, "us" means time spent in user mode | 16:08 |
| resno | user: processes that the user owns or runs | 16:08 |
| the_hydra | while "sy" is system | 16:08 |
| the_hydra | let's pick cp | 16:08 |
| the_hydra | when you copy a file with it, cp do two things actually: | 16:08 |
| the_hydra | 1. read the data from disk | 16:08 |
| the_hydra | 2. copy it to memory area, and write it somewhere | 16:09 |
| the_hydra | read and write to disk are example of system work | 16:09 |
| the_hydra | while pasting them to temporary buffer in RAM is user mode | 16:09 |
| the_hydra | or to make it simple, "sy" is anything where kernel is involved | 16:10 |
| c2tarun | the_hydra: What does it actually mean by user mode? | 16:10 |
| the_hydra | meaning, it could entirely done without kernel involved | 16:10 |
| c2tarun | ok | 16:10 |
| the_hydra | e.g: number operation (substract, multiplication) | 16:10 |
| the_hydra | so, let's bring this knowledge when observing top | 16:11 |
| the_hydra | high "us" means CPU is busy doing very likely number crunching | 16:11 |
| the_hydra | you guys got a figure what number crunching is? | 16:11 |
| obengdako | sorry guys but aren't we supposed to ask questions in the chat section because i just asked there and see others ask here | 16:11 |
| the_hydra | ok wait | 16:12 |
| the_hydra | Q: obengdako : i realise for cpu there is also ni id wa hi si st what do they mean? | 16:13 |
| the_hydra | ni is a field that tells us how much CPU time is spent to work on "niced" jobs | 16:13 |
| the_hydra | nice means any process with priority higher than 0 | 16:14 |
| the_hydra | these jobs are likely to be scheduled less frequently...because CPU prioritize bigger ones | 16:14 |
| the_hydra | id --> idle... CPU idle a.k.a resting :) | 16:15 |
| the_hydra | wa--> ok this is interesting | 16:15 |
| the_hydra | ever wonder on event like waiting cp or rsync doing large files transfer? | 16:15 |
| the_hydra | although they spent time in user and system mode, but they spend more in waiting.... | 16:16 |
| the_hydra | why wait? because the data need to be read from the disk spindle | 16:16 |
| the_hydra | reading from disk are thousands time slower rather than from RAM...so you got the picture | 16:17 |
| the_hydra | other example are waiting data from network | 16:17 |
| the_hydra | so next time you see high number it %wa, go check if an application is sitting in background doing I/O | 16:17 |
| the_hydra | Q: <obengdako> when you say higher you mean greater than zero and meaning a lower priority? | 16:18 |
| the_hydra | in priority, bigger number means lower priority | 16:18 |
| the_hydra | so +5 vs -5, -5 wins :) | 16:18 |
| the_hydra | next: si and hi... | 16:19 |
| the_hydra | they are interrupts actually | 16:19 |
| the_hydra | if it's quite big, let's say 50%, then very likely a device is "interrupting" your CPU too much | 16:20 |
| the_hydra | it could be sending data, a damaged hardware and so on | 16:20 |
| the_hydra | lately, thanks to DMA (Direct Memory access), CPU is less likely involved in hardware operation, so you can be more relaxed in regards to CPU utilization | 16:21 |
| the_hydra | Q: <obengdako> so ni will be for the higher priority stuff that have figures less than zero eg. pulseaudio at -11 | 16:21 |
| the_hydra | nope, -11 isn't accounted in %ni | 16:22 |
| the_hydra | only if e.g pulse audio is marked as +5 | 16:22 |
| the_hydra | Q: <obengdako> so would si be system interrupt and hi be hardware interrupt? | 16:23 |
| the_hydra | nope, si is "soft interrupt" | 16:23 |
| the_hydra | while "hi" is hard interrupt | 16:23 |
| the_hydra | "hi" for example is interrupt coming from your keyboard received by the CPU | 16:23 |
| the_hydra | and "si"? you can think like this: Linux kernel splits the job of taking care your hardware in two "session"...initially, in "hard interrupt" mode | 16:24 |
| the_hydra | which is done as fast as possible | 16:24 |
| the_hydra | and later, the rest is done in "soft interrupt" | 16:25 |
| the_hydra | so both represents the job when system is handling hardware most of the times | 16:25 |
| the_hydra | let me pause briefly here... | 16:25 |
| the_hydra | note: likely you will just need to watch %id | 16:26 |
| the_hydra | because, by knowing it, you could have idea how busy the CPUs are :) | 16:26 |
| the_hydra | for example, %id is 99% | 16:26 |
| the_hydra | so CPU is only busy 1% | 16:26 |
| the_hydra | press "1" to get per core/ per physical CPU statistic | 16:27 |
| the_hydra | by default what you see there is the sum of all CPUs | 16:27 |
| the_hydra | Q: <obengdako> final about ni so desktopcouch-se with ni of 10 will be accounted for in %ni and not pulseaudio with -11 ? | 16:28 |
| the_hydra | correct obengdako | 16:28 |
| the_hydra | and if you suspect slowness but you think Linux is "doing nothing", check %wa | 16:28 |
| the_hydra | if it's bigger than 0, then.....it's doing I/O e.g reading your USB thumbdrive | 16:29 |
| the_hydra | Q: <himuraken-mobile> How to switch back to sum of all cpu? | 16:29 |
| the_hydra | simple, "1" again :D | 16:30 |
| the_hydra | it's a toggle :D | 16:30 |
| the_hydra | ok, slipped something... | 16:30 |
| the_hydra | see "zombie" field? | 16:30 |
| the_hydra | got idea what that is? | 16:30 |
| the_hydra | <resno> zombies are processes that havent quit yet | 16:31 |
| the_hydra | correct... | 16:31 |
| the_hydra | so, if you see that field is bigger than zero...very likely you see bugs in the current running applications | 16:32 |
| the_hydra | to pin point it, you can use "ps" or "top" in batch mode and look out for process with "Z" status | 16:32 |
| the_hydra | such as "ps auxww | grep Z" | 16:33 |
| the_hydra | AFAIK to get rid of it, you have to kill the "master" process | 16:33 |
| the_hydra | pstree could help locate the parent of the zombie | 16:33 |
| the_hydra | Q: <obengdako> how do i use top in batch mode? | 16:34 |
| the_hydra | use -b switch | 16:34 |
| the_hydra | please note that batch mode will use any setting you have written to ~/.toprc | 16:34 |
| the_hydra | for example, you have set that you only display 20 process (by pressing "n" in top"), then in batch mode you will only see 20 process listed too | 16:35 |
| the_hydra | batch mode is an alternative way to continously monitor your system but in non interactive mode :) | 16:36 |
| the_hydra | ok, may I move to memory part? | 16:36 |
| the_hydra | you will likely think "great, all my RAM are used?" | 16:37 |
| the_hydra | "all are my app that hungry" | 16:37 |
| the_hydra | most likely no...check buffers and cached field | 16:37 |
| the_hydra | the bigger they are, meaning Linux is caching some of recently accessed files in your RAM | 16:38 |
| the_hydra | the purpose? to speed up the next access toward those files | 16:38 |
| the_hydra | Q: <resno> the_hydra: did you talk about st? | 16:39 |
| the_hydra | st is "steal" | 16:39 |
| the_hydra | what is stealed? | 16:39 |
| the_hydra | it's introduced in this virtualization hype era | 16:39 |
| the_hydra | it means some of your CPU time are accounted for doing something for the virtual machine | 16:40 |
| the_hydra | so if you run plenty virtual machines (be it KVM, Xen, Qemu in KVM mode etc), you will see this field increased | 16:40 |
| the_hydra | swap used is bigger than 0? meaning: you need more RAM... :) | 16:41 |
| the_hydra | seriously: swapping should be avoided actually...so if you have budget and can afford for bigger RAM, buy them..it will make your machine runs faster | 16:42 |
| the_hydra | these days, 2 GiB is the lowest amount of RAM you should have IMHO | 16:42 |
| === ChanServ changed the topic of #ubuntu-classroom to: Welcome to the Ubuntu Classroom - https://wiki.ubuntu.com/Classroom || Support in #ubuntu || Upcoming Schedule: http://is.gd/8rtIi || Questions in #ubuntu-classroom-chat || Current Session: How to use top and similar tools to pinpoint system problems - Instructors: the_hydra | ||
| nigelb | doh | 16:43 |
| ClassBot | resno asked: Is there a way to tell when the CPU is not keeping up. As in when more RAM wont help. | 16:46 |
| the_hydra | while %sy and %us are nice clue, for better indication use load average field | 16:47 |
| the_hydra | those three number represents loads during the last 5, 10 and 15 minutes respectively | 16:47 |
| the_hydra | but what is "load"? | 16:47 |
| the_hydra | the simplest meaning is: the average number of process running per core | 16:48 |
| the_hydra | so if you have quad core and you see -/+ 4.0, it means per core are fairly constantly running 1 process | 16:48 |
| ClassBot | obengdako asked: so if my swap is never used according to top can i delete the swap partition? | 16:49 |
| the_hydra | better not..think swap like the emergency room | 16:49 |
| the_hydra | if you have no swap and suddenly your application need more "memory", you will ended with situation called OOM (out of memory) | 16:50 |
| the_hydra | the effect? your app will be killed....:D | 16:50 |
| the_hydra | must be hurry :) | 16:50 |
| ClassBot | There are 10 minutes remaining in the current session. | 16:50 |
| the_hydra | process field....you can sort them here..press "M" to sort them by memory usage | 16:51 |
| the_hydra | and "P | 16:51 |
| the_hydra | for CPU usage | 16:51 |
| the_hydra | so if you wanna get quick idea which one is hungry for RAM...press M...then kazaam...you know it :) | 16:52 |
| the_hydra | pay attention that for finer grained statistics, you need to lower the update...press "s" and make it somewhere between 3 and 5 | 16:53 |
| the_hydra | anything higher will make top update quite slow | 16:53 |
| the_hydra | but if it is lower than that, you will make top itself one of top CPU consumer :) | 16:54 |
| the_hydra | VSZ or RSS, which one represents memory usage? | 16:54 |
| the_hydra | correct answer is RSS | 16:54 |
| the_hydra | you can think VSZ like the final plan construction of a building | 16:55 |
| the_hydra | while RSS is current progress of building construction itself | 16:55 |
| ClassBot | There are 5 minutes remaining in the current session. | 16:55 |
| the_hydra | effectively use "P" and "M" will help you to find out question like "machine feels slow, ok who's the suspect?" | 16:56 |
| the_hydra | again, questions? | 16:56 |
| ClassBot | obengdako asked: sorry but where from RSS and VSZ are they in top? or should i google? | 16:56 |
| the_hydra | oh sorry, I mean RES and VIRT | 16:57 |
| the_hydra | VIRT=virtual size (final plan construction" | 16:57 |
| the_hydra | RES= current construction progress | 16:57 |
| the_hydra | i think we got 2-3 minutes left | 16:58 |
| the_hydra | btw, press "f" in top...you have plenty choice of fields there | 16:58 |
| the_hydra | perhaps another time,I shall discuss them | 16:59 |
| ClassBot | obengdako asked: so is that like the maximum possible allocation for an app (virt) and res the current allocation? | 16:59 |
| the_hydra | not really...virt itself can expand | 16:59 |
| the_hydra | but compared to RSS, it is likely to change too frequently | 17:00 |
| the_hydra | it is not, I mean | 17:00 |
| ClassBot | Logs for this session will be available at http://irclogs.ubuntu.com/2011/01/27/%23ubuntu-classroom.html | 17:01 |
| === ChanServ changed the topic of #ubuntu-classroom to: Welcome to the Ubuntu Classroom - https://wiki.ubuntu.com/Classroom || Support in #ubuntu || Upcoming Schedule: http://is.gd/8rtIi || Questions in #ubuntu-classroom-chat || | ||
| obengdako | wow great session the_hydra | 17:01 |
| nigelb | Thanks for the wonderful session the_hydra and Happy birthday again! | 17:02 |
| the_hydra | sorry if the time feels too narrow, guys | 17:03 |
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