Differences between version 13 and predecessor to the previous major change of ProcessNotes.
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| Newer page: | version 13 | Last edited on Sunday, November 17, 2002 10:40:21 pm | by CraigBox | Revert |
| Older page: | version 1 | Last edited on Saturday, July 6, 2002 12:13:39 am | by PerryLorier | Revert |
@@ -5,16 +5,65 @@
top(1) - display the top cpu processes %%%
kill(1) - Send a signal(7) to a process by ProcessID %%%
killall(1) - Send a signal(7) to a process by name %%%
killall5(8) - Send a signal(7) to all running processes%%%
+nice(1) -run a program with modified scheduling priority%%%
pidof(8) - Tells you the pid(s) of a process by name%%%
fuser(8) - Tells you which processes are using a resource, and optionally send them a signal(7) %%%
lsof(8) - Similar to fuser
+vmstat(8) - get vm statistics and information.
-Oi! You were supposed to discuss these utilities too. Like what sets of arguments to ps are the most useful, how to display arguments to commands in top, what is wchan and why is it useful
. how nice works, what the various states of a task mean ("S","SW","R","D","<" etc),
what RSS is, running time
, how this interacts with ulimit(3). what does all the summary information that top displays mean, what other utilities (such as vmstat(8)) are useful for diagnosing problems e tc :P
+Oi! You were supposed to discuss these utilities too. Like what sets of arguments to ps are the most useful, how to display arguments to commands in top. what RSS is, how this interacts with ulimit(3).
''I'm going to, these things take time ;) -- CraigMckenna ''
+''time?! It's been months and you've not updated this page :P Bah, now I'm going to have to do it :P -- PerryLorier''
+----
+The 'TIME' column in top is the amount of time the program has spent running, not to be confused that the amount of time since the program was started. eg: a program started a month ago may have only run for 1 minute total, so it's TIME column will only show 1 minute of running time.
+----
+RSS is the ResidentSetSize, the amount of memory that the program has which is actually *in* memory (not swapped out). Note that this also covers memory which is shared between programs and threads. Mozilla for instance shows as using about 20M in 5 processes, but this doesn't mean it is using 100M in total, it means it's using about 20M in total, shared between 5 processes :)
+----
+Someone was searching for "WCHAN", so here's a definition, when a process is 'sleeping in the kernel' (in the S state) then WCHAN is the function inside the kernel it is sleeping on. for instance init(8) (at least on my machine) usually is blocked inside "select" from select(2).
+
+----
+nice(1) lets you make programs "nicer" (ie: have less access to the [CPU] in proportion to other processes). nice values in Linux range between -20 and +19. The default nice(1) level is "0". Only the root user can lower their niceless level. Higher nice level means it has a lower priority. A process running at -20 is considered "RealTime" and is never preempted.
+ nice -n ''nicelevelchange'' ''program'
+eg:
+ nice -n 1 ./program OR nice -1 ./program
+will run ./program with one level higher niceness (ie: *lower* priority compared to other processes).
+
+ nice --5 ./program
+will run a process with lower niceness (ie *higher* priority) of negative 5. (Only the root user can do this).
+----
+top(1)'s summary output:%%%
+* The top line has the uptime, the number of users logged in (according to utmp(5)) and the LoadAverage (according to uptime(1))
+* The next line has the number of processes, then a break down of sleeping processes (processes blocked waiting for an event), the number of running processes, the number of zombie processes (processes that haven't been cleaned up by their parent process) and the number of stopped processes (processes that are stopped by SIGSTOP)
+* The next line has the CPU states, amount used in userspace, the amount of CPU used in the system (kernel and device drivers), the number of cpu used by nice processes (processes that have a lower than normal priority) and the amount of cpu time that is idle (is spent with the cpu shutdown)
+* Then the memory breakdowns:
+** Total amount of physical memory that the kernel knows about
+** The amount of physical memory that is in use
+** The amount of physical memory that is not in use (wasted)
+** The amount of physical memory used for buffers (eg: networking)
+* The swap breakdown:
+** Total amount of swap space
+** Total amount of swap used
+** Total amount of swap free
+** Total amount of physical memory being used as disk cache.
+After this comes the list of processes
+
+Some hints:
+* If you're doing a lot of I/O (or especially older IDE I/O) you will probably see your "System %" increase. This means that your CPU is spending it's time talking to the hardware, and perhaps not spending much time doing whatever you want it to. If your system % is high you should perhaps consider upgrading your hardware.
+* If the number of zombies is high then you possibly have a poorly written program that doesn't cleanup zombies. use pstree(1) to get an idea which process is not cleaning up it's children.
+* See LoadAverage about the Load average and related issues.
+
+----
+The various states of a process can be:
+|^ __State__ |^ __Meaning__
+| S | Sleeping
+| W | Swapped out
+| R | Running
+| D | Blocked in a device driver in the kernel. Unkillable.
+| < | Process is running with a high priority (nice level <0)
----
also, in a related note, if you want to grep for a running process (eg foo) use:
ps ax | grep "[[f]oo"
not:
@@ -22,13 +71,13 @@
the reason for this is that the latter example will also find the "foo" in the grep command line, where as the first one can't.
----
poor mans "ps" (for when ps(1) just don't work or can't be relied upon):
- cd /proc; for i in *; do if [ -r $i/cmdline ]; then echo -n ${i}:; xargs -0 -n 1 echo -n " " <$i/cmdline; echo; fi; done
+ cd /proc; for i in *; do if [
[ -r $i/cmdline ]; then echo -n ${i}:; xargs -0 -n 1 echo -n " " <$i/cmdline; echo; fi; done
----
if your program says "Segmentation fault" (or similar), then you can retrieve information about the process when it crashed. first type
ulimit -c unlimited
-this removes the limit on dumping core files (so it should dump core now), see builtins(1) and ulimit(3) for more information about this. then run the program again. this time when it says "Segmentation fault" it will leave a file called "core" which contains the state of the program when it died. this file can be inspected by gdb ''programname'' ''corefilename''. To find out where it crashed try "bt full" at the prompt. you can also print variables to find out what they currently hold, for example "print argc" will tell you the contents of argc. of course, "quit" or C-d will exit gdb. For more information about the gnu debugger see gdb(1).
+this removes the limit on dumping core files (so it should dump core now), see builtins(1) and ulimit(3) for more information about this. then run the program again. this time when it says "Segmentation fault" it will leave a file called "core" which contains the state of the program when it died. this file can be inspected by gdb ''programname'' ''corefilename''. To find out where it crashed try "bt full" at the prompt. you can also print variables to find out what they currently hold, for example "print argc" will tell you the contents of argc. of course, "quit" or C-d will exit gdb. For more information about the gnu debugger see gdb(1). For more information about this see DeBugging
----
ps -auxww
is probably the most useful ps(1) command imho
@@ -36,13 +85,8 @@
if you want to unmount a filesystem but its in use you can use
ps -auxwwe |grep ''mountpoint''
-
-to locate any processes that are using the filesystem. CraigBox prefers
-
lsof | grep ''mountpoint''
+ fuser -vm ''mountpoint''
-lsof stands for __l__i__s__t of __o__pen __f__iles.
-
-PerryLorier prefers
- fuser -vm ''mountpoint''
+lsof(8)
stands for __l__i__s__t of __o__pen __f__iles.
