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  1. Core Server
  2. SERVER-42716

Incorrect dependency on multi-user.target causes dependency loop for systemd

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Critical - P2 Critical - P2
    • None
    • Affects Version/s: 4.0.11
    • Component/s: None
    • Labels:
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      Hello!

      I noticed quite serious issue in your official systemd unit file for MongoDB 4.0.11 in Ubuntu 18.04.

      Your current systemd unit file looks like:

      [Unit]
Description=MongoDB Database Server
After=multi-user.target
Documentation=https://docs.mongodb.org/manual[Service]
User=mongodb
Group=mongodb
EnvironmentFile=-/etc/default/mongod
ExecStart=/usr/bin/mongod --config /etc/mongod.conf
PIDFile=/var/run/mongodb/mongod.pid
# file size
LimitFSIZE=infinity
# cpu time
LimitCPU=infinity
# virtual memory size
LimitAS=infinity
# open files
LimitNOFILE=64000
# processes/threads
LimitNPROC=64000
# locked memory
LimitMEMLOCK=infinity
# total threads (user+kernel)
TasksMax=infinity
TasksAccounting=false# Recommended limits for for mongod as specified in
# http://docs.mongodb.org/manual/reference/ulimit/#recommended-settings[Install]
WantedBy=multi-user.target

      You may notice two following sections:

      After=multi-user.target
...
[Install]
WantedBy=multi-user.target

      First "After" is not required at all. Systemd will run service on multi-user.target level because you have correct configuration in "Install" section.

      And this "After=multi-user.target" dependency causes serious problems for any service which runs on same run level but requires mongodb because it creates dependency cycle which prevents proper loading of application which depend on MongoDB.

      It may happen with any application which configured this way:

      [Unit]
Description=App with MongoDB dependency 
After=mongod.service
 
[Service]
Type=forking
ExecStart=...
PIDFile=...
 
[Install]
WantedBy=multi-user.target

      It will cause following issues from systemd perspective:

      [    3.649328] systemd[1]: multi-user.target: Found ordering cycle on app.service/start
[    3.658031] systemd[1]: multi-user.target: Found dependency on mongod.service/start
[    3.665973] systemd[1]: multi-user.target: Found dependency on multi-user.target/start
[    3.674482] systemd[1]: multi-user.target: Job app.service/start deleted to break ordering cycle starting with multi-user.target/start

      Please check this issue. It's quite serious one because it causes issues for any application which depends on MongoDB.

            Assignee:
            Unassigned Unassigned
            Reporter:
            pavel.odintsov Pavel Odintsov
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              Created:
              Updated:
              Resolved: