IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 8. Open system servers - Linux for xSeries 271

8.2.5 Changing kernel parameters

The Linux kernel is the core of the operating system (OS) and is common to all Linux

distributions. You can make changes to the kernel by modifying parameters that control the

OS. These changes are made on the command line using the sysctl command.

SUSE LINUX offers a graphical method of modifying these sysctl parameters, illustrated in

Figure 8-3. To launch the powertweak tool, issue the following command:

/sbin/yast powertweak

For a text-based menu version, use the command:

/sbin/yast2 powertweak

Figure 8-3 SUSE Linux Powertweak

Red Hat offers a graphical method of modifying these sysctl parameters. To launch the tool,

issue the following command:

/usr/bin/redhat-config-proc

Figure 8-4 on page 272 shows the user interface.

Tip: By default, the kernel includes the necessary module to enable you to make changes

using sysctl without needing to reboot. However, If you choose to remove this support

(during the operating system installation), then you will have to reboot Linux before the

change can take effect.

272 IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Figure 8-4 Red Hat kernel tuning

Parameter storage locations

The kernel parameters that control how the kernel behaves are stored in /proc (and in

particular, /proc/sys).

Reading the files in the /proc directory tree provides a simple way to view configuration

parameters that are related to the kernel, processes, memory, network and other

components. Each process running in the system has a directory in /proc with the process ID

(PID) as name. Table 8-1 lists some of the files that contain kernel information.

Table 8-1 Parameters in /proc

File/directory Purpose

/proc/loadavg

Information about the load of the server in 1-minute, 5-minute, and15-minute intervals.

The uptime command gets information from this file.

/proc/kcore

(SUSE LINUX Enterprise Server only) Contains data to generate a core dump at run

time, for kernel debugging purposes. The command to create the core dump is gdb as

in:

#gdb /usr/src/linux/vmlinux /proc/kcore

/proc/stat

Kernel statistics as process, swap and disk I/O.

/proc/cpuinfo

Information about the installed CPUs.

/proc/meminfo Information about memory usage. The free command uses this information.

/proc/sys/abi/* Used to provide support for “foreign” binaries, not native to Linux: those compiled

under other UNIX variants such as SCO UnixWare 7, SCO OpenServer, and SUN

Solaris 2. By default, this support is installed, although it can be removed during

installation.