shutdown -k 如何禁用登錄？

這是（至少在 Ubuntu 上）中的-k選項文件：man shutdown

-k   Only send out the warning messages and disable 
     logins, do not actually bring  the  system down.

我最初認為這將用於pam_nologin鎖定登錄。但是，我對其進行了測試，執行後沒有看到/etc/nologincreated shutdown -k。

1. 如何shutdown -k禁用登錄？
2. 之後如何重新啟用登錄shutdown -k？

基於 Red Hat 的發行版的使用

我相信-k開關只是假裝系統正在關閉，因此會列印牆上的消息，但幾乎沒有其他作用。

  -k
      Don't halt, power-off, reboot, just write wall message.

要取消關閉事件：

$ sudo shutdown -c

來自 Ubuntu 的使用

當我嘗試在 Ubuntu 12.04 上使用上述命令時，我能夠執行以下命令：

$ sudo -i
$ strace -s 2000 -o sdown.log shutdown -k 23:00

Broadcast message from manny@manny
   (/dev/pts/1) at 20:25 ...

The system is going down for maintenance in 155 minutes!

$ shutdown -c
shutdown: Cannot find pid of running shutdown

查看strace日誌文件，sdown.log我沒有看到任何似乎表明它實際上阻止使用者登錄的任何效果。

$ grep open sdown.log
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libnih.so.1", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libnih-dbus.so.1", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libdbus-1.so.3", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/librt.so.1", O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.UTF-8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US.utf8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en_US/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.UTF-8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en.utf8/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale-langpack/en/LC_MESSAGES/upstart.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/etc/localtime", O_RDONLY|O_CLOEXEC) = 3
open("/var/run/shutdown.pid", O_RDONLY) = -1 ENOENT (No such file or directory)

所以我傾向於認為手冊頁的措辭是錯誤的，因為它說-k開關將禁用登錄。

關閉源中的錯誤？

根據@Gilles 留下的評論，他將我們定向到 的來源shutdown.c，特別是來自以下 URL：http ://packages.ubuntu.com/trusty/admin/upstart 。該shutdown實用程序目前是 Ubuntu 和 CentOS 上的 Upstart 軟體包的一部分。

查看原始碼，./util/shutdown.c請注意用於控制是否啟用/禁用使用者登錄的文件是/etc/nologin，正如您所懷疑的那樣。該文件只從函式寫入timer_callback()。這個函式然後被這個計時器作為回調呼叫：

 /* Call a timer every minute until we shutdown */
 NIH_MUST (nih_timer_add_periodic (NULL, 60,
           (NihTimerCb)timer_callback,
           message));

在函式內部有這個塊，當關閉前還剩不到 5 分鐘時，timer_callack()它似乎正在寫入文件：/etc/nologin

 /* Write /etc/nologin with less than 5 minutes remaining */
 if (delay <= 5) {
   FILE *nologin;

   nologin = fopen (ETC_NOLOGIN, "w");
   if (nologin) {
     fputs (msg, nologin);
     fclose (nologin);
   }
 }

交換機，-k僅發送警告 1 次，然後退出。

 { 'k', NULL, N_("only send warnings, don't shutdown"),
   NULL, NULL, &warn_only, NULL },

這裡退出：

 if (warn_only)
   exit (0);

引用自：https://unix.stackexchange.com/questions/125800