《OneinStack》安装JAVA环境，跑一段时间，却换一般用户（www）部署代码时候，提示报错信息：-sh: fork failed - too many processes或者su: cannot set user id: Resource temporarily unavailable，明显是系统资源受限制。
排查问题过程如下：
1. 关闭www下所有应用
为了安全JAVA应用跑在一般用户（www），由于报错，切换www用户，提示系统资源限制，于是关闭www用户下所有应用，使能切换到www用户下，方便排除问题。
2. 查看www用户配置文件ulimit参数
[root@OneinStack ~]# su - www
[www@OneinStack ~]$ 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) 256345
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 65535
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
[root@OneinStack ~]# su - www
[www@OneinStack ~]$ 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) 256345
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 65535
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 1024
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
从上面可以看出，系统默认max user processes为1024，显然就是这个问题。
3. 查看系统ulimit全局参数
[root@OneinStack ~]# grep -v ^# /etc/security/limits.conf
* soft nproc 65535
* hard nproc 65535
* soft nofile 65535
* hard nofile 65535
[root@OneinStack ~]# grep -v ^# /etc/security/limits.conf
* soft nproc 65535
* hard nproc 65535
* soft nofile 65535
* hard nofile 65535
奇怪，通过系统ulimit全局参数看，*代表所有用户，www用户竟然还有限制，于是Google获知，REHL6下引入配置文件/etc/security/limits.d/90-nproc.conf（可参考：https://bugzilla.redhat.com/show_bug.cgi?id=919793）
注：也可能是其它命名，如Linode修改为：/etc/security/limits.d/20-nproc.conf
4. 修改/etc/security/limits.d/90-nproc.conf
[root@OneinStack ~]# grep -v ^# /etc/security/limits.d/90-nproc.conf
* soft nproc 1024
root soft nproc unlimited
[root@OneinStack ~]# grep -v ^# /etc/security/limits.d/90-nproc.conf
* soft nproc 1024
root soft nproc unlimited
问题就在这里，这里限制为1024
修改为65535，保持文件如下：
[root@OneinStack ~]# grep -v ^# /etc/security/limits.d/90-nproc.conf
* soft nproc 65535
root soft nproc unlimited
退出当前用户，重新登录即可让之前修改的limits生效，执行如下命令发现修改成功
[root@OneinStack ~]# su - www
[www@OneinStack ~]$ 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) 256345
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 65535
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 65535
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
启动java应用，问题解决
注：如果使用*号让全局用户生效是受文件/etc/security/limits.d/90-nproc.conf中nproc值大小制约的，而如果仅仅是针对某个用户，那么就不受该文件nproc值大小的影响。
Wed Aug 26 14:55:49 CST 2015
1. 关闭www下所有应用
2. 查看www用户配置文件ulimit参数
3. 查看系统ulimit全局参数
4. 修改/etc/security/limits.d/90-nproc.conf目录
