[root@gitlab ~]# gitlab-ctl reconfigure
.........
.........
STDERR: sysctl: cannot open "/etc/sysctl.d/90-omnibus-gitlab-kernel.sem.conf": No such file or directory
sysctl: cannot open "/etc/sysctl.d/90-omnibus-gitlab-net.core.somaxconn.conf": No such file or directory
---- End output of sysctl -e --system ----
Ran sysctl -e --system returned 255

问题原因分析：
丢失了报错中的这两个配置文件，进入/etc/sysctl.d目录发现，这两个文件都是通过链接到/opt/gitlab/embedded/etc/目录下。
然而/opt/gitlab/embedded/etc/确实没有这两个文件

[root@gitlab ~]# ll /etc/sysctl.d/
total 0
lrwxrwxrwx  1 root root 58 Nov 10 22:23 90-omnibus-gitlab-kernel.sem.conf -> /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.sem.conf
lrwxrwxrwx  1 root root 61 Nov 10 22:23 90-omnibus-gitlab-kernel.shmall.conf -> /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.shmall.conf
lrwxrwxrwx  1 root root 61 Nov 10 22:23 90-omnibus-gitlab-kernel.shmmax.conf -> /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.shmmax.conf
lrwxrwxrwx  1 root root 66 Nov 10 22:25 90-omnibus-gitlab-net.core.somaxconn.conf -> /opt/gitlab/embedded/etc/90-omnibus-gitlab-net.core.somaxconn.conf
lrwxrwxrwx. 1 root root 14 Oct 30 09:13 99-sysctl.conf -> ../sysctl.conf
  
[root@gitlab ~]# ll /opt/gitlab/embedded/etc
total 12
-rw-r--r-- 1 root root  24 Apr 12 23:18 90-omnibus-gitlab-kernel.shmall.conf
-rw-r--r-- 1 root root  28 Apr 12 23:17 90-omnibus-gitlab-kernel.shmmax.conf
-rwxr-xr-x 1 root root 196 Apr 12 23:16 gitconfig
  
[root@gitlab ~]# ll /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.sem.conf
ls: cannot access /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.sem.conf: No such file or directory
[root@gitlab ~]# ll /opt/gitlab/embedded/etc/90-omnibus-gitlab-net.core.somaxconn.conf
ls: cannot access /opt/gitlab/embedded/etc/90-omnibus-gitlab-net.core.somaxconn.conf: No such file or directory
  
解决方法一：
从别的备份机（或者在别的机器上重新安装一次，"gitlab-ctl reconfigure"之后生成这两个文件）将这两个文件拷贝回来！
  
解决方法二：
[root@gitlab ~]# vim /etc/gitlab/gitlab.rb
# unicorn['port'] = 8080
修改为：
unicorn['port'] = 8090
  
之后重新加载配置文件
[root@gitlab ~]# gitlab-ctl reconfigure
  
再次会报错，然后再修改/etc/gitlab/gitlab.rb，修改为原来的配置
[root@gitlab ~]# vim /etc/gitlab/gitlab.rb
# unicorn['port'] = 8080
  
再次重新加载配置文件就OK了！
[root@gitlab ~]# gitlab-ctl reconfigure
  
再次查看，发现上面配置中报错的两个文件已经存在了
[root@gitlab ~]# ll /opt/gitlab/embedded/etc/
total 20
-rw-r--r-- 1 root root  30 Apr 12 23:33 90-omnibus-gitlab-kernel.sem.conf
-rw-r--r-- 1 root root  24 Apr 12 23:18 90-omnibus-gitlab-kernel.shmall.conf
-rw-r--r-- 1 root root  28 Apr 12 23:17 90-omnibus-gitlab-kernel.shmmax.conf
-rw-r--r-- 1 root root  26 Apr 12 23:35 90-omnibus-gitlab-net.core.somaxconn.conf
-rwxr-xr-x 1 root root 196 Apr 12 23:16 gitconfig
[root@gitlab ~]# ll /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.sem.conf
-rw-r--r-- 1 root root 30 Apr 12 23:33 /opt/gitlab/embedded/etc/90-omnibus-gitlab-kernel.sem.conf
[root@gitlab ~]# ll /opt/gitlab/embedded/etc/90-omnibus-gitlab-net.core.somaxconn.conf
-rw-r--r-- 1 root root 26 Apr 12 23:35 /opt/gitlab/embedded/etc/90-omnibus-gitlab-net.core.somaxconn.conf
  
最后再启动gitlab
[root@gitlab ~]# gitlab-ctl start