Ubuntu18.04 Apacheが強制終了する場合

Apache が突然死するので、ログを見てみると

$ tail /var/log/apache2/error.log

[Mon Sep 03 19:24:17.252747 2018] [mpm_prefork:emerg] [pid 7851] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.253264 2018] [mpm_prefork:emerg] [pid 7819] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.253385 2018] [mpm_prefork:emerg] [pid 7815] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.253561 2018] [mpm_prefork:emerg] [pid 7817] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.253739 2018] [mpm_prefork:emerg] [pid 7852] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.253916 2018] [mpm_prefork:emerg] [pid 7855] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.252992 2018] [mpm_prefork:emerg] [pid 7848] (43)Identifier removed: AH00144: couldn't grab the accept mutex
[Mon Sep 03 19:24:17.464946 2018] [core:alert] [pid 7636] AH00050: Child 7815 returned a Fatal error... Apache is exiting!
[Mon Sep 03 19:24:17.464976 2018] [:emerg] [pid 7636] AH02818: MPM run failed, exitin

となっていた。

Apache 2.4 で AH00144: couldn't grab the accept mutex | gwaw.jp
https://www.gwaw.jp/20180526-16.html

こちらを参考に

$ sudo bash -c "echo 'Mutex file:\${APACHE_LOCK_DIR} default' > /etc/apache2/conf-available/mutex-file.conf"

して

$ sudo a2enconf mutex-file
$ sudo systemctl restart apache2

した。