Thanks for your suggestions. I still don't see any clues about what's going on.
It seems that it fails if I leave the server running for a while and then try to restart it, but it works if I've just restarted it recently. Here's the output of journalctl: $ sudo journalctl -u apache2.service | tail Jul 25 17:54:42 physionet1.ecg.mit.edu systemd[1]: Stopping LSB: Apache2 web server... Jul 25 17:54:43 physionet1.ecg.mit.edu apache2[26339]: Stopping web server: apache2. Jul 25 17:54:43 physionet1.ecg.mit.edu systemd[1]: Starting LSB: Apache2 web server... Jul 25 17:54:44 physionet1.ecg.mit.edu apache2[26363]: Starting web server: apache2. Jul 25 17:54:44 physionet1.ecg.mit.edu systemd[1]: Started LSB: Apache2 web server. Jul 26 00:02:02 physionet1.ecg.mit.edu apache2[803]: Stopping web server: apache2. Jul 27 14:30:48 physionet1.ecg.mit.edu systemd[1]: Starting LSB: Apache2 web server... Jul 27 14:30:48 physionet1.ecg.mit.edu apache2[11430]: Starting web server: apache2. Jul 27 14:30:51 physionet1.ecg.mit.edu apache2[11439]: Stopping web server: apache2. Jul 27 14:30:51 physionet1.ecg.mit.edu systemd[1]: Started LSB: Apache2 web server. $ sudo service apache2 status ● apache2.service - LSB: Apache2 web server Loaded: loaded (/etc/init.d/apache2) Drop-In: /lib/systemd/system/apache2.service.d └─forking.conf Active: inactive (dead) since Thu 2017-07-27 14:30:51 EDT; 3min 22s ago Process: 11439 ExecStop=/etc/init.d/apache2 stop (code=exited, status=0/SUCCESS) Process: 11430 ExecStart=/etc/init.d/apache2 start (code=exited, status=0/SUCCESS) Jul 27 14:30:48 physionet1.ecg.mit.edu apache2[11430]: Starting web server: apache2. Jul 27 14:30:51 physionet1.ecg.mit.edu apache2[11439]: Stopping web server: apache2. Jul 27 14:30:51 physionet1.ecg.mit.edu systemd[1]: Started LSB: Apache2 web server. The same messages also appear in /var/log/daemon.log and /var/log/syslog; there's nothing more after 'Started LSB: Apache2 web server'. apache error log shows a message at shutdown, but nothing for starting up: $ sudo tail /var/log/apache2/error.log $ sudo tail /var/log/apache2/error.log.1 [Thu Jul 27 00:13:06.420511 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:07.421537 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:08.422584 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:09.423615 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:10.424641 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:11.425616 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:12.426582 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:13.427615 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 00:13:14.428661 2017] [mpm_event:error] [pid 20472:tid 140057478371200] AH00485: scoreboard is full, not at MaxRequestWorkers [Thu Jul 27 14:30:50.574596 2017] [mpm_event:notice] [pid 20472:tid 140057478371200] AH00491: caught SIGTERM, shutting down Here is the 'term.log' from upgrading deb8u9 -> deb8u10, nothing looks unusual: Log started: 2017-07-19 15:18:07 (Reading database ... ^M(Reading database ... 5%^M(Reading database ... 10%^M(Reading database ... 15%^M(Reading database ... 20%^M(Re ading database ... 25%^M(Reading database ... 30%^M(Reading database ... 35%^M(Reading database ... 40%^M(Reading database ... 45%^M(R eading database ... 50%^M(Reading database ... 55%^M(Reading database ... 60%^M(Reading database ... 65%^M(Reading database ... 70%^M( Reading database ... 75%^M(Reading database ... 80%^M(Reading database ... 85%^M(Reading database ... 90%^M(Reading database ... 95%^M (Reading database ... 100%^M(Reading database ... 97551 files and directories currently installed.) Preparing to unpack .../apache2-mpm-event_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2-mpm-event (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../apache2.2-bin_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2.2-bin (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../apache2_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2 (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../apache2-bin_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2-bin (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../apache2-utils_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2-utils (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../apache2-data_2.4.10-10+deb8u10_all.deb ... Unpacking apache2-data (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../libmagickwand-6.q16-2_8%3a6.8.9.9-5+deb8u10_amd64.deb ... Unpacking libmagickwand-6.q16-2:amd64 (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Preparing to unpack .../libmagickcore-6.q16-2_8%3a6.8.9.9-5+deb8u10_amd64.deb ... Unpacking libmagickcore-6.q16-2:amd64 (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Preparing to unpack .../imagemagick-common_8%3a6.8.9.9-5+deb8u10_all.deb ... Unpacking imagemagick-common (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Preparing to unpack .../apache2.2-common_2.4.10-10+deb8u10_amd64.deb ... Unpacking apache2.2-common (2.4.10-10+deb8u10) over (2.4.10-10+deb8u9) ... Preparing to unpack .../imagemagick_8%3a6.8.9.9-5+deb8u10_amd64.deb ... Unpacking imagemagick (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Preparing to unpack .../imagemagick-6.q16_8%3a6.8.9.9-5+deb8u10_amd64.deb ... Unpacking imagemagick-6.q16 (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Preparing to unpack .../libmagickcore-6.q16-2-extra_8%3a6.8.9.9-5+deb8u10_amd64.deb ... Unpacking libmagickcore-6.q16-2-extra:amd64 (8:6.8.9.9-5+deb8u10) over (8:6.8.9.9-5+deb8u9) ... Processing triggers for systemd (215-17+deb8u7) ... Processing triggers for man-db (2.7.0.2-5) ... Processing triggers for desktop-file-utils (0.22-1) ... Processing triggers for mime-support (3.58) ... Processing triggers for hicolor-icon-theme (0.13-1) ... Setting up apache2-bin (2.4.10-10+deb8u10) ... Setting up apache2-utils (2.4.10-10+deb8u10) ... Setting up apache2-data (2.4.10-10+deb8u10) ... Setting up apache2 (2.4.10-10+deb8u10) ... Setting up apache2-mpm-event (2.4.10-10+deb8u10) ... Setting up apache2.2-bin (2.4.10-10+deb8u10) ... Setting up imagemagick-common (8:6.8.9.9-5+deb8u10) ... Setting up libmagickcore-6.q16-2:amd64 (8:6.8.9.9-5+deb8u10) ... Setting up libmagickwand-6.q16-2:amd64 (8:6.8.9.9-5+deb8u10) ... Setting up apache2.2-common (2.4.10-10+deb8u10) ... Setting up imagemagick-6.q16 (8:6.8.9.9-5+deb8u10) ... Setting up imagemagick (8:6.8.9.9-5+deb8u10) ... Setting up libmagickcore-6.q16-2-extra:amd64 (8:6.8.9.9-5+deb8u10) ... Processing triggers for libc-bin (2.19-18+deb8u10) ... Log ended: 2017-07-19 15:18:48