Recipe ID: hsts-r60
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One of the most important responsibilities a system administrator has, is monitoring their systems. As a system administrator you'll need the ability to find out what is happening on your system at any given time. Whether it's the percentage of system's resources currently used, what commands are being run, or who is logged on. This article will cover how to monitor your system, and in some cases, how to resolve problems that may arise.
When a performance issue arises, there are 4 main areas to consider: CPU, Memory, Disk I/O, and Network. The ability to determine where the bottleneck is can save you a lot of time.
1. System Resources
Being able to monitor the performance of your system is essential. If system resources become to low it can cause a lot of problems. System resources can be taken up by individual users, or by services your system may host such as email or web pages. The ability to know what is happening can help determine whether system upgrades are needed, or if some services need to be moved to another machine.
1.1. The top command.
The most common of these commands is top. The top will display a continually updating report of system resource usage.
12:10:49 up 1 day, 3:47, 7 users, load average: 0.23, 0.19, 0.10
125 processes: 105 sleeping, 2 running, 18 zombie, 0 stopped
CPU states: 5.1% user 1.1% system 0.0% nice 0.0% iowait 93.6% idle
Mem: 512716k av, 506176k used, 6540k free, 0k shrd, 21888k buff
Swap: 1044216k av, 161672k used, 882544k free 199388k cached
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME CPU COMMAND
The top portion of the report lists information such as the system time, uptime, CPU usage, physical ans swap memory usage, and number of processes. Below that is a list of the processes sorted by CPU utilization.
You can modify the output of top while is is running. If you hit an i, top will no longer display idle processes. Hit i again to see them again. Hitting M will sort by memory usage, S will sort by how long they processes have been running, and P will sort by CPU usage again.
In addition to viewing options, you can also modify processes from within the top command. You can use u to view processes owned by a specific user, k to kill processes, and r to reboot them.
For more in-depth information about processes you can look in the /proc filesystem. In the /proc filesystem you will find a series of sub-directories with numeric names. These directories are associated with the processes ids of currently running processes. In each directory you will find a series of files containing information about the process.
YOU MUST TAKE EXTREME CAUTION TO NOT MODIFY THESE FILES, DOING SO MAY CAUSE SYSTEM PROBLEMS!
1.2. The iostat command.
The iostat will display the current CPU load average and disk I/O information. This is a great command to monitor your disk I/O usage.
Linux 2.4.20-24.9 (myhost) 12/23/2003
avg-cpu: %user %nice %sys %idle
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
For 2.4 kernels the devices is names using the device's major and minor number. In this case the device listed is /dev/hda. To have iostat print this out for you, use the -x.
# iostat -x
Linux 2.4.20-24.9 (myhost) 12/23/2003
avg-cpu: %user %nice %sys %idle
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
The iostat man page contains a detailed explanation of what each of these columns mean.
1.3. The ps command
The ps will provide you a list of processes currently running. There is a wide variety of options that this command gives you.
A common use would be to list all processes currently running. To do this you would use the ps -ef command. (Screen output from this command is too large to include, the following is only a partial output.)
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Dec22 ? 00:00:03 init
root 2 1 0 Dec22 ? 00:00:00 [keventd]
root 3 1 0 Dec22 ? 00:00:00 [kapmd]
root 4 1 0 Dec22 ? 00:00:00 [ksoftirqd_CPU0]
root 9 1 0 Dec22 ? 00:00:00 [bdflush]
root 5 1 0 Dec22 ? 00:00:00 [kswapd]
root 6 1 0 Dec22 ? 00:00:00 [kscand/DMA]
root 7 1 0 Dec22 ? 00:01:28 [kscand/Normal]
root 8 1 0 Dec22 ? 00:00:00 [kscand/HighMem]
root 10 1 0 Dec22 ? 00:00:00 [kupdated]
root 11 1 0 Dec22 ? 00:00:00 [mdrecoveryd]
root 15 1 0 Dec22 ? 00:00:01 [kjournald]
root 81 1 0 Dec22 ? 00:00:00 [khubd]
root 1188 1 0 Dec22 ? 00:00:00 [kjournald]
root 1675 1 0 Dec22 ? 00:00:00 syslogd -m 0
root 1679 1 0 Dec22 ? 00:00:00 klogd -x
rpc 1707 1 0 Dec22 ? 00:00:00 portmap
root 1813 1 0 Dec22 ? 00:00:00 /usr/sbin/sshd
ntp 1847 1 0 Dec22 ? 00:00:00 ntpd -U ntp
root 1930 1 0 Dec22 ? 00:00:00 rpc.rquotad
root 1934 1 0 Dec22 ? 00:00:00 [nfsd]
root 1942 1 0 Dec22 ? 00:00:00 [lockd]
root 1943 1 0 Dec22 ? 00:00:00 [rpciod]
root 1949 1 0 Dec22 ? 00:00:00 rpc.mountd
root 1961 1 0 Dec22 ? 00:00:00 /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf
root 2057 1 0 Dec22 ? 00:00:00 /usr/bin/spamd -d -c -a
root 2066 1 0 Dec22 ? 00:00:00 gpm -t ps/2 -m /dev/psaux
bin 2076 1 0 Dec22 ? 00:00:00 /usr/sbin/cannaserver -syslog -u bin
root 2087 1 0 Dec22 ? 00:00:00 crond
daemon 2195 1 0 Dec22 ? 00:00:00 /usr/sbin/atd
root 2215 1 0 Dec22 ? 00:00:11 /usr/sbin/rcd
weeksa 3414 3413 0 Dec22 pts/1 00:00:00 /bin/bash
weeksa 4342 3413 0 Dec22 pts/2 00:00:00 /bin/bash
weeksa 19121 18668 0 12:58 pts/2 00:00:00 ps -ef
The first column shows who owns the process. The second column is the process ID. The Third column is the parent process ID. This is the process that generated, or started, the process. The forth column is the CPU usage (in percent). The fifth column is the start time, of date if the process has been running long enough. The sixth column is the tty associated with the process, if applicable. The seventh column is the cumulative CPU usage (total amount of CPU time is has used while running). The eighth column is the command itself.
With this information you can see exactly what is running on your system and kill run-away processes, or those that are causing problems.
1.4. The vmstat command
The vmstat command will provide a report showing statistics for system processes, memory, swap, I/O, and the CPU. These statistics are generated using data from the last time the command was run to the present. In the case of the command never being run, the data will be from the last reboot until the present.
procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 0 0 181604 17000 26296 201120 0 2 8 24 149 9 61 3 36
The following was taken from the vmstat man page.
r: The number of processes waiting for run time.
b: The number of processes in uninterruptable sleep.
w: The number of processes swapped out but otherwise runnable. This
field is calculated, but Linux never desperation swaps.
swpd: the amount of virtual memory used (kB).
free: the amount of idle memory (kB).
buff: the amount of memory used as buffers (kB).
si: Amount of memory swapped in from disk (kB/s).
so: Amount of memory swapped to disk (kB/s).
bi: Blocks sent to a block device (blocks/s).
bo: Blocks received from a block device (blocks/s).
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.
These are percentages of total CPU time.
us: user time
sy: system time
id: idle time
1.5. The lsof command
The lsof command will print out a list of every file that is in use. Since Linux considers everything a file, this list can be very long. However, this command can be useful in diagnosing problems. An example of this is if you wish to unmount a filesystem, but you are being told that it is in use. You could use this command and grep for the name of the filesystem to see who is using it.
Or suppose you want to see all files in use by a particular process. To do this you would use lsof -p -processid-.
1.6. Finding More Utilities
There are lots of online resources for learning what tools are out there and how to do a number of tasks with them.
2. Filesystem Usage
Many reports are currently talking about how cheap storage has gotten, but if you're like most of us it isn't cheap enough. Most of us have a limited amount of space, and need to be able to monitor it and control how it's used.
2.1. The df command
The df is the simplest tool available to view disk usage. Simply type in df and you'll be shown disk usage for all your mounted filesystems in 1K blocks
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/hda3 5242904 759692 4483212 15% /
tmpfs 127876 8 127868 1% /dev/shm
/dev/hda1 127351 33047 87729 28% /boot
/dev/hda9 10485816 33508 10452308 1% /home
/dev/hda8 5242904 932468 4310436 18% /srv
/dev/hda7 3145816 32964 3112852 2% /tmp
/dev/hda5 5160416 474336 4423928 10% /usr
/dev/hda6 3145816 412132 2733684 14% /var
You can also use the -h to see the output in "human-readable" format. This will be in K, Megs, or Gigs depending on the size of the filesystem. Alternately, you can also use the -B to specify block size.
In addition to space usage, you could use the -i option to view the number of used and available inodes.
user@server:~> df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/hda3 0 0 0 - /
tmpfs 31969 5 31964 1% /dev/shm
/dev/hda1 32912 47 32865 1% /boot
/dev/hda9 0 0 0 - /home
/dev/hda8 0 0 0 - /srv
/dev/hda7 0 0 0 - /tmp
/dev/hda5 656640 26651 629989 5% /usr
/dev/hda6 0 0 0 - /var
2.2. The du command
Now that you know how much space has been used on a filesystem how can you find out where that data is? To view usage by a directory or file you can use du. Unless you specify a filename du will act recursively. For example:
user@server:~> du file.txt
Or like the df I can use the -h and get the same output in "human-readable" form.
user@server:~> du -h file.txt
Unless you specify a filename du will act recursively.
user@server:~> du -h /usr/local
If you just want a summary of that directory you can use the -s option.
user@server:~> du -hs /usr/local
You can find more information about quotas online.
3. Monitoring Users
Just because you're paranoid doesn't mean they AREN'T out to get you... Source Unknown
From time to time there are going to be occasions where you will want to know exactly what people are doing on your system. Maybe you notice that a lot of RAM is being used, or a lot of CPU activity. You are going to want to see who is on the system, what they are running, and what kind of resources they are using.
3.1. The who command
The easiest way to see who is on the system is to do a who or w. The --> who is a simple tool that lists out who is logged --> on the system and what port or terminal they are logged on at.
bjones pts/0 May 23 09:33
wally pts/3 May 20 11:35
aweeks pts/1 May 22 11:03
aweeks pts/2 May 23 15:04
3.2. The ps command -again!
In the previous section we can see that user aweeks is logged onto both pts/1 and pts/2, but what if we want to see what they are doing? We could to a ps -u aweeks and get the following output
user@server:~> ps -u aweeks
20876 pts/1 00:00:00 bash
20904 pts/2 00:00:00 bash
20951 pts/2 00:00:00 ssh
21012 pts/1 00:00:00 ps
From this we can see that the user is doing a ps ssh.
This is a much more consolidated use of the ps than discussed previously.
3.3. The w command
Even easier than using the who and ps -u commands is to use the w. w will print out not only who is on the system, but also the commands they are running.
aweeks :0 09:32 ?xdm? 30:09 0.02s -:0
aweeks pts/0 09:33 5:49m 0.00s 0.82s kdeinit: kded
aweeks pts/2 09:35 8.00s 0.55s 0.36s vi sag-0.9.sgml
aweeks pts/1 15:03 59.00s 0.03s 0.03s /bin/bash
From this we can see that I have a kde session running, I'm working in this document :-), and have another terminal open sitting idle at a bash prompt.
Resources for Linux Kernel Programmers
Linux File System Dictionary
Comprehensive Review of How Linux File and Directory System Works
Hands-on Linux classes
Linux Operating System Distributions
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