Linux Tuning Parameters September 28th, 2010
KernelTo successfully run enterprise applications, such as a database server, on your Linux distribution, you may be required to update some of the default kernel parameter settings. For example, the 2.4.x series kernel message queue parameter msgmni has a default value (for example, shared memory, or shmmax is only 33,554,432 bytes on Red Hat Linux by default) that allows only a limited number of simultaneous connections to a database. Here are some recommended values (by the IBM DB2 Support Web site) for database servers to run optimally:
|- kernel.shmmax=268435456 for 32-bit- kernel.shmmax=1073741824 for 64-bit- kernel.msgmni=1024- fs.file-max=8192- kernel.sem=”250 32000 32 1024″|
|To view current settings, run command:# more /proc/sys/kernel/shmmaxTo set it to a new value for this running session, which takes effect immediately, run command:# echo 268435456 > /proc/sys/kernel/shmmaxTo set it to a new value permanently (so it survives reboots), modify the sysctl.conf file:…kernel.shmmax = 268435456…|
|To view current settings, run command:# more /proc/sys/kernel/sem 250 32000 32 1024 To set it to a new value for this running session, which takes effect immediately, run command:# echo 500 512000 64 2048 > /proc/sys/kernel/semParameters meaning:SEMMSL – semaphores per IDSEMMNS – (SEMMNI*SEMMSL) max semaphores in systemSEMOPM – max operations per semop callSEMMNI – max semaphore identifiers|
|To view current settings, run command:# ulimit -aTo set it to a new value for this running session, which takes effect immediately, run command:# ulimit -n 8800# ulimit -n -1 // for unlimited; recommended if server isn’t shared
Alternatively, if you want the changes to survive reboot, do the following:
- Exit all shell sessions for the user you want to change limits on.- As root, edit the file /etc/security/limits.conf and add these two lines toward the end: user1 soft nofile 16000 user1 hard nofile 20000 ** the two lines above changes the max number of file handles – nofile – to new settings.- Save the file.- Login as the user1 again. The new changes will be in effect.
|To view current settings, run command:# more /proc/sys/kernel/msgmni# more /proc/sys/kernel/msgmaxTo set it to a new value for this running session, which takes effect immediately, run command:# echo 2048 > /proc/sys/kernel/msgmni# echo 64000 > /proc/sys/kernel/msgmax|
NetworkGigabit-based network interfaces have many performance-related parameters inside of their device driver such as CPU affinity. Also, the TCP protocol can be tuned to increase network throughput for connection-hungry applications.
|To view current TCP settings, run command:# sysctl net.ipv4.tcp_keepalive_timenet.ipv4.tcp_keepalive_time = 7200 // 2 hourswhere net.ipv4.tcp_keepalive_time is a TCP tuning parameter.To set a TCP parameter to a value, run command:# sysctl -w net.ipv4.tcp_keepalive_time=1800A list of recommended TCP parameters, values, and their meanings:Tuning Parameter Tuning Value Description of impact ——————————————————————————net.ipv4.tcp_tw_reuse net.ipv4.tcp_tw_recycle 1 Reuse sockets in the time-wait state —net.core.wmem_max 8388608 Increase the maximum write buffer queue size —net.core.rmem_max 8388608 Increase the maximum read buffer queue size —net.ipv4.tcp_rmem 4096 87380 8388608 Set the minimum, initial, and maximum sizes for the read buffer. Note that this maximum should be less than or equal to the value set in net.core.rmem_max. —net.ipv4.tcp_wmem 4096 87380 8388608 Set the minimum, initial, and maximum sizes for the write buffer. Note that this maximum should be less than or equal to the value set in net.core.wmem_max. —timeout_timewait echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
Determines the time that must elapse before TCP/IP can release a closed connection and reuse its resources. This interval between closure and release is known as the TIME_WAIT state or twice the maximum segment lifetime (2MSL) state. During this time, reopening the connection to the client and server cost less than establishing a new connection. By reducing the value of this entry, TCP/IP can release closed connections faster, providing more resources for new connections. Adjust this parameter if the running application requires rapid release, the creation of new connections, and a low throughput due to many connections sitting in the TIME_WAIT state.
Disk I/OChoose the Right File SystemUse ‘ext3′ file system in Linux.
- It is enhanced version of ext2
- With journaling capability – high level of data integrity (in event of unclean shutdown)
- It does not need to check disks on unclean shutdown and reboot (time consuming)
- Faster write – ext3 journaling optimizes hard drive head motion
|# mke2fs -j -b 2048 -i 4096 /dev/sdamke2fs 1.32 (09-Nov-2002)/dev/sda is entire device, not just one partition!Proceed anyway? (y,n) yFilesystem label=OS type: LinuxBlock size=2048 (log=1)Fragment size=2048 (log=1)13107200 inodes, 26214400 blocks1310720 blocks (5.00%) reserved for the super userFirst data block=01600 block groups16384 blocks per group, 16384 fragments per group8192 inodes per groupSuperblock backups stored on blocks: 16384, 49152, 81920, 114688, 147456, 409600, 442368, 802816, 1327104, 2048000, 3981312, 5619712, 10240000, 11943936
Writing inode tables: doneWriting superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 28 mounts or180 days, whichever comes first. Use tune2fs -c or -i to override.
Use ‘noatime’ File System Mount OptionUse ‘noatime’ option in the file system boot-up configuration file ‘fstab’. Edit the fstab file under /etc. This option works the best if external storage is used, for example, SAN:
|# more /etc/fstabLABEL=/ / ext3 defaults 1 1none /dev/pts devpts gid=5,mode=620 0 0none /proc proc defaults 0 0none /dev/shm tmpfs defaults 0 0/dev/sdc2 swap swap defaults 0 0/dev/cdrom /mnt/cdrom udf,iso9660 noauto,owner,kudzu,ro 0 0/dev/fd0 /mnt/floppy auto noauto,owner,kudzu 0 0/dev/sda /database ext3 defaults,noatime 1 2/dev/sdb /logs ext3 defaults,noatime 1 2/dev/sdc /multimediafiles ext3 defaults,noatime 1 2|
Tune the Elevator Algorithm in Linux Kernel for Disk I/OAfter choosing the file system, there are several kernel and mounting options that can affect it. One such kernel setting is the elevator algorithm. Tuning the elevator algorithm helps the system balance the need for low latency with the need to collect enough data to efficiently organize batches of read and write requests to the disk. The elevator algorithm can be adjusted with the following command:
|# elvtune -r 1024 -w 2048 /dev/sda/dev/sda elevator ID 2 read_latency: 1024 write_latency: 2048 max_bomb_segments: 6 The parameters are: read latency (-r), write latency (-w) and the device affected. Red Hat recommends using a read latency half the size of the write latency (as shown). As usual, to make this setting permanent, add the ‘elvtune’ command to the /etc/rc.d/rc.local script.|
OthersDisable Unnecessary Daemons (They Take up Memory and CPU)There are daemons (background services) running on every server that are probably not needed. Disabling these daemons frees memory, decreases startup time, and decreases the number of processes that the CPU has to handle. A side benefit to this is increased security of the server because fewer daemons mean fewer exploitable processes.
|Some example Linux daemons running by default (and should be disabled). Use command:#/sbin/chkconfig –levels 2345 sendmail off #/sbin/chkconfig sendmail off|
|apmd||Advanced power management daemon|
|autofs||Automatically mounts file systems on demand (i.e.: mounts a CD-ROM automatically)|
|cups||Common UNIX� Printing System|
|hpoj||HP OfficeJet support|
|isdn||ISDN modem support|
|netfs||Used in support of exporting NFS shares|
|nfslock||Used for file locking with NFS|
|pcmcia||PCMCIA support on a server|
|rhnsd||Red Hat Network update service for checking for updates and security errata|
|sendmail||Mail Transport Agent|
|xfs||Font server for X Windows|
Shutdown GUINormally, there is no need for a GUI on a Linux server. All administration tasks can be achieved by the command line, redirecting the X display or through a Web browser interface. Modify the ‘inittab’ file to set boot level as 3: To set the initial runlevel (3 instead of 5) of a machine at boot, modify the /etc/inittab file
This entry was posted on Tuesday, September 28th, 2010 at 9:54 pm and is filed under CentOS, debian, fedora, feebsd, linux, Networking, ubuntu. You can follow any responses to this entry through the RSS 2.0 feed.You can leave a response, or trackback from your own site.