首先出现这个提示的原因：应用程序打开的文件数量超过了系统设定值。

如何查看当前系统每个用户最大允许打开文件数量：

[root@registry ~]# 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) 3820
max locked memory (kbytes, -l) 64
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) 3820
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

或者

[root@registry ~]# ulimit -n
1024　　

其中 open files (-n) 1024 表示每个用户最大允许打开的文件数量是1024

#查看一下当前已有的连接数，以此来判断open files 为1024 是否足够

[root@registry ~]# lsof -n |awk '{print$2}'|sort |uniq -c |sort -nr |more
590 5458
445 1065
306 638
267 770
190 5682
189 5457
158 704
130 1194
117 681
81 1263
68 5419
66 640
62 1
60 5677
57 678
55 1067
51 9036
51 1196
48 5698
44 677
44 470
38 494
32 637
29 4430
20 4614
17 9250
14 4566
12 9256
12 9251
11 9254
11 9252
10 9255
10 693
9 9253
3 92
3 9037
3 9033
3 9
3 8964
3 8
3 726

其中第一列是打开的文件句柄数量，第二列是进程id号

通过句柄数量最多的进程，查看是哪个应用程序打开了最多的文件句柄，通过命令：

[root@registry ~]# ps -aef |grep PID

设置open files 数值的方法

1.临时设置方法

[root@registry ~]# ulimit -n 4096
[root@registry ~]# 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) 3820
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 4096
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) 3820
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

这样就可以把当前用户的最大允许打开文件数量设置为4096，但这种设置方法在重启后会还原为默认值。

2.永久设置方法

[root@registry ~]# vim /etc/security/limits.conf

End of file

root soft nofile 65535
root hard nofile 65535
* soft nofile 65535
* hard nofile 65535

在文件末尾添加上述四行，其中后面两行的 * 表示所有的用户，也可以根据需要设置某一个用户，比如www

# End of file
root soft nofile 65535
root hard nofile 65535
www soft nofile 65535
www hard nofile 65535

注销账户，重新登录即可生效。　

如果想查看某个进程最大允许打开的文件数量，可通过如下命令查看：

[root@registry ~]# top
top - 15:39:21 up 101 days, 6:26, 1 user, load average: 0.33, 0.57, 0.52
Tasks: 70 total, 1 running, 69 sleeping, 0 stopped, 0 zombie
%Cpu(s): 6.7 us, 0.0 sy, 0.0 ni, 93.3 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 3881824 total, 111956 free, 3505012 used, 264856 buff/cache
KiB Swap: 2047996 total, 1001156 free, 1046840 used. 123968 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
12872 www 20 0 2738092 743948 2292 S 6.7 19.2 652:05.43 java
1 root 20 0 43380 2244 1352 S 0.0 0.1 4:11.26 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.31 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 28:18.97 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
7 root rt 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh
9 root 20 0 0 0 0 S 0.0 0.0 33:52.08 rcu_sched
10 root rt 0 0 0 0 S 0.0 0.0 0:39.61 watchdog/0
12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
13 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 netns
14 root 20 0 0 0 0 S 0.0 0.0 0:07.72 khungtaskd
15 root 0 -20 0 0 0 S 0.0 0.0 0:00.18 writeback
16 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kintegrityd
17 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 bioset
18 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kblockd
19 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 md
25 root 20 0 0 0 0 S 0.0 0.0 12:21.57 kswapd0
26 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
27 root 39 19 0 0 0 S 0.0 0.0 0:17.32 khugepaged
28 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 crypto
36 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kthrotld
38 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kmpath_rdacd
39 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kpsmoused
40 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 ipv6_addrconf
59 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 deferwq
101 root 20 0 0 0 0 S 0.0 0.0 0:03.48 kauditd
225 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 ata_sff
233 root 20 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_0
234 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 scsi_tmf_0
235 root 20 0 0 0 0 S 0.0 0.0 0:00.00 scsi_eh_1
236 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 scsi_tmf_1
240 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 ttm_swap
252 root 0 -20 0 0 0 S 0.0 0.0 1:07.64 kworker/0:1H
257 root 20 0 0 0 0 S 0.0 0.0 3:12.26 jbd2/vda1-8
258 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 ext4-rsv-conver
325 root 20 0 119080 5460 5316 S 0.0 0.1 5:27.58 systemd-journal
354 root 20 0 44032 8 4 S 0.0 0.0 0:00.08 systemd-udevd
[root@registry ~]# cat /proc/12872/limits
Limit 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 65535 65535 processes
Max open files 65535 65535 files
Max locked memory 65536 65536 bytes
Max address space unlimited unlimited bytes
Max file locks unlimited unlimited locks
Max pending signals 15089 15089 signals
Max msgqueue size 819200 819200 bytes
Max nice priority 0 0
Max realtime priority 0 0
Max realtime timeout unlimited unlimited us