Ubuntu 中修改文件权限是说Operation not permitted

chmod 755 /etc/ssh/sshd_config
chmod: changing permissions of '/etc/ssh/sshd_config': Operation not permitted

应该是禁用了修改权限，检查命令 lsattr
例如
 lsattr /etc/ssh/sshd_config
----i---------e------- /etc/ssh/sshd_config

去除i权限
chattr -i /etc/ssh/sshd_config
再检查
lsattr /etc/ssh/sshd_config
--------------e------- /etc/ssh/sshd_config

可以愉快的修改了。