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Managing CPU Utilization

TOP COMMAND
# top


You can see Linux CPU utilization under CPU stats. The task’s share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time. In a true SMP environment (multiple CPUS), top will operate in number of CPUs. Please note that you need to type q key to exit the top command display.

The top command produces a frequently-updated list of processes. By default, the processes are ordered by percentage of CPU usage, with only the "top" CPU consumers shown. The top command shows how much processing power and memory are being used, as well as other information about the running processes.

# sysstat

# mpstat

If you are using SMP (Multiple CPU) system, use mpstat command to display the utilization of each CPU individually. It report processors related statistics. For example, type command:

# mpstat

-----------------------------

Linux 2.6.15.4 (debian)         Thursday 06 April 2006

05:13:05  IST  CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal   %idle    intr/s
05:13:05  IST  all   16.52    0.00    2.87    1.09    0.07    0.02    0.00   79.42    830.06

-----------------------------

# mpstat -P ALL
Shows all the CPU's processing details.


CPU utilization using sar command

You can display today’s CPU activity, with sar command:

# sar

-----------------------------

Linux 2.6.9-42.0.3.ELsmp (dellbox.xyz.co.in)         01/13/2007

12:00:02 AM       CPU     %user     %nice   %system   %iowait     %idle
12:10:01 AM       all      1.05      0.00      0.28      0.04     98.64
12:20:01 AM       all      0.74      0.00      0.34      0.38     98.54
12:30:02 AM       all      1.09      0.00      0.28      0.10     98.53
12:40:01 AM       all      0.76      0.00      0.21      0.03     99.00
12:50:01 AM       all      1.25      0.00      0.32      0.03     98.40
01:00:01 AM       all      0.80      0.00      0.24      0.03     98.92
...
.....
..
04:40:01 AM       all      8.39      0.00     33.17      0.06     58.38
04:50:01 AM       all      8.68      0.00     37.51      0.04     53.78
05:00:01 AM       all      7.10      0.00     30.48      0.04     62.39
05:10:01 AM       all      8.78      0.00     37.74      0.03     53.44
05:20:02 AM       all      8.30      0.00     35.45      0.06     56.18
Average:          all      3.09      0.00      9.14      0.09     87.68
-----------------------------
# sar -u 2 5

Where,

• -u 12 5 : Report CPU utilization. The following values are displayed:
• %user: Percentage of CPU utilization that occurred while executing at the user level (application).
• %nice: Percentage of CPU utilization that occurred while executing at the user level with nice priority.
• %system: Percentage of CPU utilization that occurred while executing at the system level (kernel).
• %iowait: Percentage of time that the CPU or CPUs were idle during which the system had an outstanding disk I/O request.
• %idle: Percentage of time that the CPU or CPUs were idle and the system did not have an outstanding disk I/O request.

To get multiple samples and multiple reports set an output file for the sar command. Run the sar command as a background process using.

# sar -o output.file 12 8 >/dev/null 2>&1 &

Better use nohup command so that you can logout and check back report later on:

# nohup sar -o output.file 12 8 >/dev/null 2>&1 &

All data is captured in binary form and saved to a file (data.file). The data can then be selectively displayed ith the sar command using the -f option.

# sar -f data.file

Find out who is monopolizing or eating the CPUs

Finally, you need to determine which process is monopolizing or eating the CPUs. Following command will displays the top 10 CPU users on the Linux system.

# ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10
OR
# ps -eo pcpu,pid,user,args | sort -r -k1 | less

-----------------------------

%CPU   PID USER     COMMAND
96  2148 kiran    /usr/lib/vmware/bin/vmware-vmx -C /var/lib/vmware/Virtual Machines/Ubuntu 64-bit/Ubuntu 64-bit.vmx -@ ""
0.7  3358 mysql    /usr/libexec/mysqld --defaults-file=/etc/my.cnf --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --skip-locking --socket=/var/lib/mysql/mysql.sock
0.4 29129 lighttpd /usr/bin/php
0.4 29128 lighttpd /usr/bin/php
0.4 29127 lighttpd /usr/bin/php
0.4 29126 lighttpd /usr/bin/php
0.2  2177 vivek    [vmware-rtc]
0.0     9 root     [kacpid]
0.0     8 root     [khelper]

-----------------------------




Extending a logical volume

To extend a logical volume you simply tell the lvextend command how much you want to increase the size. You can specify how much to grow the volume, or how large you want it to grow to:

# lvextend -L12G /dev/myvg/homevol lvextend -- extending logical volume "/dev/myvg/homevol" to 12 GB lvextend -- doing automatic backup of volume group "myvg" lvextend -- logical volume "/dev/myvg/homevol" successfully extended

will extend /dev/myvg/homevol to 12 Gigabytes.

# lvextend -L+1G /dev/myvg/homevol lvextend -- extending logical volume "/dev/myvg/homevol" to 13 GB lvextend -- doing automatic backup of volume group "myvg" lvextend -- logical volume "/dev/myvg/homevol" successfully extended

will add another gigabyte to /dev/myvg/homevol.

After you have extended the logical volume it is necessary to increase the file system size to match. how you do this depends on the file system you are using.

By default, most file system resizing tools will increase the size of the file system to be the size of the underlying logical volume so you don't need to worry about specifying the same size for each of the two commands.

1. ext2/ext3

   Unless you have patched your kernel with the ext2online patch it is necessary to unmount the file system before resizing it. (It seems that the online resizing patch is rather dangerous, so use at your own risk)

   # umount /dev/myvg/homevol/dev/myvg/homevol # resize2fs /dev/myvg/homevol # mount /dev/myvg/homevol /home

   If you don't have e2fsprogs 1.19 or later, you can download the ext2resize command from ext2resize.sourceforge.net and use that:

   # umount /dev/myvg/homevol/dev/myvg/homevol # ext2resize /dev/myvg/homevol # mount /dev/myvg/homevol /home

   For ext2 there is an easier way. LVM 1 ships with a utility called e2fsadm which does the lvextend and resize2fs for you (it can also do file system shrinking, see the next section).

   	LVM 2 Caveat
   	There is currently no e2fsadm equivalent for LVM 2 and the e2fsadm that ships with LVM 1 does not work with LVM 2.

   so the single command

   # e2fsadm -L+1G /dev/myvg/homevol

   is equivalent to the two commands:

   # lvextend -L+1G /dev/myvg/homevol # resize2fs /dev/myvg/homevol

   	Note
   	You will still need to unmount the file system before running e2fsadm.

2. reiserfs

   Reiserfs file systems can be resized when mounted or unmounted as you prefer:

   • Online:

     # resize_reiserfs -f /dev/myvg/homevol

   • Offline:

     # umount /dev/myvg/homevol # resize_reiserfs /dev/myvg/homevol # mount -treiserfs /dev/myvg/homevol /home

3. xfs

   XFS file systems must be mounted to be resized and the mount-point is specified rather than the device name.

   # xfs_growfs /home

4. jfs

   Just like XFS the JFS file system must be mounted to be resized and the mount-point is specified rather than the device name. You need at least Version 1.0.21 of the jfs-utils to do this.

   # mount -o remount,resize /home

   Known Kernel Bug

   Some kernel versions have problems with this syntax (2.6.0 is known to have this problem). In this case you have to explicitly specify the new size of the filesystem in blocks. This is extremely error prone as you must know the blocksize of your filesystem and calculate the new size based on those units. Example: If you were to resize a JFS file system to 4 gigabytes that has 4k blocks, you would write: # mount -o remount,resize=1048576 /home