如题：
修改这个文件就行了：/etc/security/limits.conf
查看当前配置的方法：
1. 找到httpd的pid（中间那三个apache的）
[root@server-tong-1 ~]# ps -ef |grep httpdroot ?????1234 ????1 ?0 03:21 ? ???????00:00:00 /usr/sbin/httpd -DFOREGROUNDapache ???1235 ?1234 ?0 03:21 ? ???????00:00:00 /usr/sbin/httpd -DFOREGROUNDapache ???1236 ?1234 ?0 03:21 ? ???????00:00:00 /usr/sbin/httpd -DFOREGROUNDapache ???1237 ?1234 ?0 03:21 ? ???????00:00:00 /usr/sbin/httpd -DFOREGROUNDapache ???1239 ?1234 ?0 03:21 ? ???????00:00:00 /usr/sbin/httpd -DFOREGROUNDroot ?????1537 ?1210 ?0 03:28 pts/0 ???00:00:00 grep --color=auto httpd
2. 查看这几个进程当前使用的值
[root@server-tong-1 ~]# cat /proc/1236/limitsLimit ????????????????????Soft Limit ??????????Hard Limit ??????????Units ????Max cpu time ?????????????unlimited ???????????unlimited ???????????seconds ??Max file size ????????????unlimited ???????????unlimited ???????????bytes ????Max data size ????????????unlimited ???????????unlimited ???????????bytes ????Max stack size ???????????8388608 ?????????????unlimited ???????????bytes ????Max core file size ???????0 ???????????????????unlimited ???????????bytes ????Max resident set ?????????unlimited ???????????unlimited ???????????bytes ????Max processes ????????????15072 ???????????????15072 ???????????????processes Max open files ???????????1024 ????????????????4096 ????????????????files ????Max locked memory ????????65536 ???????????????65536 ???????????????bytes ????Max address space ????????unlimited ???????????unlimited ???????????bytes ????Max file locks ???????????unlimited ???????????unlimited ???????????locks ????Max pending signals ??????15072 ???????????????15072 ???????????????signals ??Max msgqueue size ????????819200 ??????????????819200 ??????????????bytes ????Max nice priority ????????0 ???????????????????0 ???????????????????Max realtime priority ????0 ???????????????????0 ???????????????????Max realtime timeout ?????unlimited ???????????unlimited ???????????us ???
3. 查看系统允许修改的最大值，以及用户名
[root@server-tong-1 ~]# cat /etc/shadow |grep apaapache:!!:17833::::::[root@server-tong-1 ~]# cat /proc/sys/fs/nr_open 1048576
查到，limit可以使用的最大值是1048576，用户名是apache
另外，需要提到的一点，我曾经尝试直接将这个值设置成unlimited, 结果导致了root无法登录。【大哭～～】，后来想办法进去之后，查看到报错如下：【tag：修改limit.conf之后 ssh失败 root无法登录 OS无法登录】
546 Dec 10 02:44:03 server-tong-1 login: pam_limits(login:session): Could not set limit for ‘nofile‘: Operation not permitted547 Dec 10 02:44:03 server-tong-1 login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)548 Dec 10 02:44:03 server-tong-1 login: Permission denied549 Dec 10 02:44:15 server-tong-1 login: pam_limits(login:session): Could not set limit for ‘nofile‘: Operation not permitted550 Dec 10 02:44:15 server-tong-1 login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)551 Dec 10 02:44:15 server-tong-1 login: Permission denied552 Dec 10 02:44:42 server-tong-1 login: pam_limits(login:session): Could not set limit for ‘nofile‘: Operation not permitted553 Dec 10 02:44:42 server-tong-1 login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)554 Dec 10 02:44:42 server-tong-1 login: Permission denied555 Dec 10 02:44:55 server-tong-1 login: pam_unix(login:auth): check pass; user unknown556 Dec 10 02:44:55 server-tong-1 login: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=tty1 ruser= rhost=557 Dec 10 02:44:57 server-tong-1 login: FAILED LOGIN 1 FROM tty1 FOR (unknown), User not known to the underlying authentication module558 Dec 10 02:45:03 server-tong-1 login: pam_limits(login:session): Could not set limit for ‘nofile‘: Operation not permitted559 Dec 10 02:45:03 server-tong-1 login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)560 Dec 10 02:45:03 server-tong-1 login: Permission denied561 Dec 10 02:50:01 server-tong-1 crond[14616]: pam_limits(crond:session): Could not set limit for ‘nofile‘: Operation not permitted562 Dec 10 03:00:01 server-tong-1 crond[14649]: pam_limits(crond:session): Could not set limit for ‘nofile‘: Operation not permitted563 Dec 10 03:00:20 server-tong-1 sshd[784]: Received signal 15; terminating.
4. 准备就绪后，我们现在来修改limit.conf文件吧！追加两行配置如下，并重启OS
[root@server-tong-1 ~]# tail -n3 /etc/security/limits.conf apache hard nofile 1048576apache soft nofile 1048576# End of file[root@server-tong-1 ~]#
5. 用2中的方法查看修改是否成功。
完！
[httpd][daily] 查看并修改httpd的最大fd打开个数limit
原文地址：https://www.cnblogs.com/hugetong/p/10095524.html