RHEL7/CentOS 7でCtrl-Alt-Delを無効にする

デフォルトではCtrl-Alt-Delでサーバが再起動します。これを無効にする方法です。

参考サイト
How to disable Ctrl-Alt-Del in RHEL7 ?
https://access.redhat.com/solutions/1123873
この情報もRHNアカウントでログインしないと全文が読めません。
こう言う技術情報はだれでも閲覧できるようにしてもいいと思うけど、まあRHNアカウントは無料で作成できるから、読みたい人はすでに持っているかな。

試しに下記で検証してみました。
・CentOS Linux release 7.6.1810 (Core)
・Kernel 3.10.0-957.10.1.el7.x86_64

Ctrl-Alt-Delを試してみると即座にサーバが再起動されました。
ログ(/var/log/messages)を見ると”Received SIGINT”と記録されて再起動が始まっています。

• ctrl-alt-delを無効
Shell

# systemctl mask ctrl-alt-del.target Created symlink from /etc/systemd/system/ctrl-alt-del.target to /dev/null.

1 2	# systemctl mask ctrl-alt-del.target Created symlink from /etc/systemd/system/ctrl-alt-del.target to /dev/null.

ログにctrl-alt-delは失敗と記録されていました。

Apr 15 17:31:41 centos7 systemd: Received SIGINT. Apr 15 17:31:41 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked.

1 2	Apr 15 17:31:41 centos7 systemd: Received SIGINT. Apr 15 17:31:41 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked.

ただしこの設定でも2秒間にCtrl-Alt-Delが7回以上実行(SIGINTが発生)すれば再起動が行われます。

Apr 15 17:55:48 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked. Apr 15 17:55:48 centos7 systemd: Received SIGINT. Apr 15 17:55:48 centos7 systemd: Forcibly rebooting: Ctrl-Alt-Del was pressed more than 7 times within 2s Apr 15 17:55:48 centos7 systemd: Shutting down. Apr 15 17:55:48 centos7 systemd-shutdown[1]: Syncing filesystems and block devices. Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpuset Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpu Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpuacct

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Apr 15 17:55:48 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked. Apr 15 17:55:48 centos7 systemd: Received SIGINT. Apr 15 17:55:48 centos7 systemd: Forcibly rebooting: Ctrl-Alt-Del was pressed more than 7 times within 2s Apr 15 17:55:48 centos7 systemd: Shutting down. Apr 15 17:55:48 centos7 systemd-shutdown[1]: Syncing filesystems and block devices. Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpuset Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpu Apr 15 17:55:57 centos7 kernel: Initializing cgroup subsys cpuacct

# man systemd SIGNALS SIGINT Upon receiving this signal the systemd system manager will start the ctrl-alt-del.target unit. This is mostly equivalent to systemctl start ctl-alt-del.target. If this signal is received more often than 7 times per 2s an immediate reboot is triggered. Note that pressing Ctrl-Alt-Del on the console will trigger this signal. Hence, if a reboot is hanging pressing Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way to trigger an immediate reboot.

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# man systemd SIGNALS        SIGINT            Upon receiving this signal the systemd system manager will start the ctrl-alt-del.target            unit. This is mostly equivalent to systemctl start ctl-alt-del.target. If this signal is            received more often than 7 times per 2s an immediate reboot is triggered. Note that pressing            Ctrl-Alt-Del on the console will trigger this signal. Hence, if a reboot is hanging pressing            Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way to trigger an immediate            reboot.

• RHEL 7.4以降ではCtrlAltDelBurstActionが追加

RHEL 7.4以降では上記の2秒間に7回の動作を設定するできるCtrlAltDelBurstAction=が追加されました。

Shell

# man systemd-system.conf OPTIONS CtrlAltDelBurstAction= Defines what action will be performed if user presses Ctrl-Alt-Delete more than 7 times in 2s. Can be set to "reboot-force", "poweroff-force", "reboot-immediate", "poweroff-immediate" or disabled with "none". Defaults to "reboot-force".

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# man systemd-system.conf OPTIONS        CtrlAltDelBurstAction=            Defines what action will be performed if user presses Ctrl-Alt-Delete more than 7 times in            2s. Can be set to "reboot-force", "poweroff-force", "reboot-immediate", "poweroff-immediate"            or disabled with "none". Defaults to "reboot-force".

“reboot-force”, “poweroff-force”, “reboot-immediate”, “poweroff-immediate”が設定できて、無効にする場合は”none”、デフォルトは”reboot-force”です。

無効にしてみます。

Shell

[root@centos7 ~]# grep CtrlAltDelBurstAction /etc/systemd/system.conf #CtrlAltDelBurstAction=reboot-force [root@centos7 ~]# vi /etc/systemd/system.conf [root@centos7 ~]# grep CtrlAltDelBurstAction /etc/systemd/system.conf #CtrlAltDelBurstAction=reboot-force CtrlAltDelBurstAction=none

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[root@centos7 ~]# grep CtrlAltDelBurstAction /etc/systemd/system.conf #CtrlAltDelBurstAction=reboot-force [root@centos7 ~]# vi /etc/systemd/system.conf [root@centos7 ~]# grep CtrlAltDelBurstAction /etc/systemd/system.conf #CtrlAltDelBurstAction=reboot-force CtrlAltDelBurstAction=none

コンソールでctrl-alt-delを連打してみましたがログに記録されますが、再起動はされませんでした。


Apr 15 18:22:22 centos7 systemd: Received SIGINT. Apr 15 18:22:22 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked.

1 2	Apr 15 18:22:22 centos7 systemd: Received SIGINT. Apr 15 18:22:22 centos7 systemd: Failed to enqueue ctrl-alt-del.target job: Unit is masked.