設定 vm.vfs_cache_pressure 使 kernel 更勤於回收 cache。
sysctl -w vm.vfs_cache_pressure=n (n > 100)
]}}
== System Performance Tuning : File System ==
* 如何調整每個使用者可以開啟的檔案個數
* [參考] [http://www.xenoclast.org/doc/benchmark/HTTP-benchmarking-HOWTO/node7.html Increasing the file descriptor limit]
* [參考] [http://www.netadmintools.com/art295.html GNU/Linux - How Many Open Files?]
* 注意：修改 /etc/security/limits.conf 中間必須確定是 TAB ，如果有設定 vim 的 softwaretab 的話，得特別當心!!!
* /proc/sys/fs/file-max - 核心預設最多可以開啟的檔案個數
{{{
~$ cat /proc/sys/fs/file-max
743964
}}}
* 修改方法: 使用 sysctl 指令或編輯 /etc/sysctl.conf
{{{
sysctl -w fs.file-max=100000
}}}
* /proc/sys/fs/file-nr - 目前已開啟檔案個數、可供開啟檔案個數、總開啟檔案上限
{{{
[root@srv-4 proc]# cat /proc/sys/fs/file-nr
3391 969 52427
| | |
| | |
| | maximum open file descriptors
| total free allocated file descriptors
total allocated file descriptors
(the number of file descriptors allocated since boot)
}}}
* /etc/security/limits.conf - 每個程序(process)可以開啟檔案的個數(number limits of open files per process) - 像 HDFS 的 !DataNode 就需要調整這種參數([wiki:jazz/10-02-22#Hadoop:HDFS 2010-02-22])
{{{
#!diff
--- /etc/security/limits.conf 2010-02-22 11:29:11.000000000 +0800
+++ /etc/security/limits.conf.new 2010-02-22 11:28:33.000000000 +0800
@@ -49,4 +49,6 @@
#ftp - chroot /ftp
#@student - maxlogins 4
+* soft nofile 4096
+* hard nofile 743964
+
# End of file
}}}
* /etc/pam.d/login - 告訴系統要用 /etc/security/limits.conf 來設定一些上限
{{{
# Sets up user limits according to /etc/security/limits.conf
# (Replaces the use of /etc/limits in old login)
session required pam_limits.so
}}}
* 指令: ulimit - 可以告訴你一些系統限制，並且設定想要的値
{{{
jazz@Wdebian:~$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 72704
max locked memory (kbytes, -l) 32
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 72704
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
}}}
* 假設 /proc/sys/fs/file-max 跟 /etc/security/limits.conf 都有設定上限為 743964，且 /etc/pam.d/login 也有打開，但是 ulimit -a 指令仍顯示 1024 (預設)，可以修改 /etc/rc.local 或 /etc/profile 強制用 ulimit -n 743964 來提高開檔個數。
{{{
~$ ulimit -n 743964
}}}
* [備註] 如果 ulimit 超出可容許範圍，會顯示 Operation not permitted，此時請檢查相關設定値
{{{
~$ ulimit -n 7439640
-bash: ulimit: open files: cannot modify limit: Operation not permitted
}}}
== I/O Performance Tuning : NFS ==
* NFS Tuning - /etc/fstab - 加大 NFS read/write size 可以提升檔案系統的 I/O 效率 ([wiki:krg_tuning 2008-03-20 (rock/rider)])
{{{
192.168.0.111:/home /home nfs rw,bg,soft,intr,rsize=262144,wsize=262144 0 4
192.168.0.111:/opt /opt nfs ro,bg,soft,intr,rsize=262144,wsize=262144 0 4
192.168.0.111:/usr /usr nfs ro,bg,soft,intr,rsize=262144,wsize=262144 0 4
}}}
== I/O Performance Tuning : IOWait ==
* [wiki:jazz/10-03-31 2010-03-31] : 高 IOWait 有什麼好的解決之道呢??
* [http://www.scriptbits.net/2009/07/how-to-identify-what-processes-are-generating-io-wait-load/ How to identify what processes are generating IO Wait load?]
{{{
Jun run "pidstat -d 5" and it will print the list of processes doing IO over the last 5 seconds.
}}}
* [http://ubuntuforums.org/showthread.php?t=1382161 Re: Major problems: High Iowait. Change filesystem from etx4 to xfs/ext3/jfs?]
{{{
vm.dirty_writeback_centisecs=100
vm.dirty_expire_centisecs=100"
}}}
* [http://ubuntuforums.org/showthread.php?t=200004 iowait problem] - 顯示了使用 vmstat , iostat , hdparm 的技巧
== Network Performance Tuning ==
* TCP Tuning - ([wiki:krg_tuning 2008-03-20 (LSI)])
{{{
echo 262144 > /proc/sys/net/core/rmem_default
echo 8388608 > /proc/sys/net/core/wmem_max
echo 8388608 > /proc/sys/net/core/rmem_max
echo "4096 87380 4194304" > /proc/sys/net/ipv4/tcp_rmem
echo "4096 65536 4194304" > /proc/sys/net/ipv4/tcp_wmem
}}}
* TCP TIME_WAIT & Reuse - 適用網站伺服器 ([wiki:jazz/Trac_Updates#a2010-03-26 2010-03-26])
{{{
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
sysctl net.ipv4.tcp_tw_reuse=1
sysctl net.ipv4.tcp_tw_recycle=1
}}}
* 如果沒辦法 ping 224.0.0.1 的話，代表 Broadcast ICMP 封包被濾掉了，因為預設 Linux kernel 2.6 是 disable 的。解法如下：([wiki:jazz/09-09-07 2009-09-07])
{{{
echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
}}}
{{{
~# echo "net.ipv4.icmp_echo_ignore_broadcasts = 0" >> /etc/sysctl.conf
~# sysctl -p
net.ipv4.ip_forward = 1
net.ipv4.icmp_echo_ignore_broadcasts = 0
}}}
* [http://fourdollars.blogspot.com/2009/04/linux-system.html 如何在 Linux System 當中偵測網路線是否有接上？] ([wiki:jazz/09-05-05 2009-05-05])
{{{
$ cat /sys/class/net/eth0/carrier
}}}
== Power Management ==
* 啟動 SATA ALPM 電源管理功能 - [http://packages.debian.org/powertop powertop] 提供之建議
{{{
echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
}}}
* 虛擬機器的 clocksource ([wiki/jazz/Trac_Updates#a2010-02-11 2010-02-11])
{{{
echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource
}}}
* 直接修改系統參數讓 Linux 休眠 ([wiki:rock/drbl_switch 2010-03-03 (rock)])
{{{
# echo 4 > /proc/acpi/sleep /** 適用 Kernel 2.4 (swsusp)**/
# echo disk > /sys/power/state /** 適用 Kernel 2.4 & 2.6 (swsusp)**/
}}}
== Security ==
* 關於 /proc/sysrq-trigger ([wiki:jazz/09-11-17 2009-11-17])
* [http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/s2-proc-sysrq-trigger.html Redhat 手冊的說明 - /proc/sysrq-trigger]
* 其實除了 CTRL+ALT+DEL 外，Linux 還可以透過 [http://en.wikipedia.org/wiki/SysRq System Request (Sys Rq) 按鍵] 來做一些特殊除錯工作。這個 Sys Rq 鍵，通常跟 Print Screen 鍵做在一起。
* 要啟用這個功能，首先必須確認核心的 CONFIG_MAGIC_SYSRQ 參數是否有 enable。
* [http://en.wikipedia.org/wiki/Magic_SysRq_key 維基百科除了說明 SYSRQ 可以做哪些事情]外，還介紹了[http://julien.danjou.info/sysrqd/ sysrqd]這個軟體，讓管理者可以遠端執行 SYSRQ 的指令。PS.[http://packages.debian.org/sysrqd sysrqd 也有 debian 套件]!!
* 關於 /proc/sys/kernel/sysrq ([wiki:jazz/09-11-17 2009-11-17])
* [http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/en-US/Reference_Guide/s3-proc-sys-kernel.html Redhat 手冊的說明 - /proc/sys/kernel/ 底下的檔案意涵]
* [http://lxr.linux.no/#linux+v2.6.31/Documentation/sysrq.txt Linux 核心關於 SysRq 的說明]
