今天下午，一个web集群节点碰到了一个以前没有遇到过的问题，Apache2.0.54无法启动，察看error.log发觉有这样一行错误：
[emerg] (28)No space left on device: Couldn't create accept lock
刚开始还以为是空间不足，造成无法创建cgisock文件，但是df -h察看，发觉不是这个问题。求助于google，真是好帮手，一下子就找到了原因。
使用： ipcs -s | grep nobody 察看发觉有一堆ipc使用，需要干掉。这个可能的原因是程序所造成的。
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清除命令：
ipcs -s | grep nobody | perl -e 'while (<STDIN>) { @a=split(/\s+/); print `ipcrm sem $a[1]`}'
然后启动Apache即可。
更深入的了解：
Fixing Apache "No space left on device: Couldn't create accept lock" errors
Error Message: When starting Apache, I get this error message in the main Apache error_log:
[emerg] (28)No space left on device: Couldn't create accept lock
[notice] suEXEC mechanism enabled (wrapper: /usr/sbin/suexec)
[notice] Digest: generating secret for digest authentication ...
[notice] Digest: done
[warn] pid file /etc/httpd/run/httpd.pid overwritten -- Unclean shutdown of previous Apache run?
[emerg] (28)No space left on device: Couldn't create accept lock
First off, check to make sure that you really aren't out of disk space, or have hit a quota limit. Another way that Apache can create the "accept lock" is with a semaphore. A semaphore is an inter-process communication tool that is used by Apache to communicate with it's child processes. This error message may mean that Apache couldn't create a new semaphore.
Check to see how many semaphores are currently in use. If Apache is running correctly, you should see something like this:
# ipcs -s
------ Semaphore Arrays --------
key semid owner perms nsems
0x00000000 68681743 apache 600 1
0x00000000 68714515 apache 600 1
0x00000000 68747291 apache 600 1
If Apache is stopped, and you still see these semaphores, then you can safely kill them by running this command for each semaphore id (in the second column)
$ ipcrm -s <semid>
To destroy all semaphores, you can run this from the command line (with "apache" being the apache-user):
for semid in `ipcs -s | grep nobody | cut -f2 -d" "`;
do ipcrm -s $semid; done
[ 这个地方可能需要改一下, 我的apache是nobody启的，所以是grep nobody
If you are out of semaphores
If you can't create any more semaphores:
Sometimes your system may need to increase the number of semaphores that are available on the system. This requires a change to a kernel parameter. If you are running on a virtual server and cannot modify kernel parameters, you may need to ask your hosting provider to change this parameter on their host server To view the current parameters:
# ipcs -l
------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 32768
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1
------ Semaphore Limits --------
max number of arrays = 1024
max semaphores per array = 250
max semaphores system wide = 256000
max ops per semop call = 32
semaphore max value = 32767
------ Messages: Limits --------
max queues system wide = 1024
max size of message (bytes) = 8192
default max size of queue (bytes) = 16384
To change these parameters, modify the file /etc/sysctl.conf and add the following lines:
kernel.msgmni = 1024
kernel.sem = 250 256000 32 1024
Then load these settings with the command:
sysctl -p
Your Apache process should now be able to create the needed semaphores and run properly
这里介绍下kernel.msgmni
/proc/sys/kernel/msgmni
该文件指定消息队列标识的最大数目，即系统范围内最大多少个消息队列。
缺省设置：16
在 root 下用 sysctl kernel.msgmni 检查该参数， 也可以在命令行下
sysctl -w kernel.msgmni=XXX 重新设定。
