在linux vps，偶尔会出现错误bash: fork: Cannot allocate memory。这是vps的bug，虽然你可能还有很多内存没有用完。怎么办？最理想的办法就是重启vps，不想重启怎么办？看下面的操作过程：

[root@www.654z.com]# more database.php
-bash: fork: Cannot allocate memory
[root@www.654z.com]# free
-bash: fork: Cannot allocate memory
[root@www.654z.com]# reboot
-bash: fork: Cannot allocate memory
[root@www.654z.com]# service httpd stop
-bash: fork: Cannot allocate memory
[root@www.654z.com]# service httpd stop
-bash: fork: Cannot allocate memory
[root@www.654z.com]# service httpd stop
-bash: fork: Cannot allocate memory
[root@www.654z.com]# service httpd stop
-bash: fork: Cannot allocate memory
[root@www.654z.com]# service httpd stop
-bash: fork: Cannot allocate memory
[root@www.654z.com]# top
-bash: fork: Cannot allocate memory
[root@www.654z.com]# free
-bash: fork: Cannot allocate memory

连free命令都无法执行。reboot也无法执行。怎么办？等待几分钟再试一试。我等了3分钟，然后发现free可以用了。这时候别大意，全部重启一下apache/mysql等，这样就可以稳定一段时间了：

[root@www.654z.com]# free
             total       used       free     shared    buffers     cached
Mem:        524800     245908     278892          0          0          0
-/+ buffers/cache:     245908     278892
Swap:            0          0          0
[root@www.654z.com]# service httpd stop
Stopping httpd: [  OK  ]
[root@www.654z.com]# free
             total       used       free     shared    buffers     cached
Mem:        524800      81272     443528          0          0          0
-/+ buffers/cache:      81272     443528
Swap:            0          0          0
[root@www.654z.com]# top

top - 11:27:04 up 11 days,  6:16,  2 users,  load average: 1.53, 0.63, 0.48
Tasks:  20 total,   1 running,  19 sleeping,   0 stopped,   0 zombie 
Cpu(s):  6.2%us,  0.6%sy,  0.0%ni, 88.1%id,  5.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:    524800k total,    81656k used,   443144k free,        0k buffers