Understanding container logging

The container application does not connect to a STDOUT, which is why logs, by default, are written to the container
Use docker logs mycontainer to get access to the container log
Using docker logs is convenient for troubleshooting

Demo

Output


controlplane $ docker run -d mariadb
5c2398dbcbfff2d400f4a3d910e32a3f8ab75171641fb60366e7f95ec259a214
controlplane $ docker ps -a
CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS                      PORTS                                   NAMES
5c2398dbcbff   mariadb   "docker-entrypoint.s…"   6 seconds ago    Exited (1) 4 seconds ago                                            xander

As you can see the mariadb container exited with status code 1 i.e., with error. To check for logs to inspect the error use docker logs.

Output


controlplane $ docker logs xander
2024-10-18 22:18:28+00:00 [Note] [Entrypoint]: Entrypoint script for MariaDB Server 1:11.5.2+maria~ubu2404 started.
2024-10-18 22:18:29+00:00 [Warn] [Entrypoint]: /sys/fs/cgroup/cpuset:/system.slice/docker-5c2398dbcbfff2d400f4a3d910e32a3f8ab75171641fb60366e7f95ec259a214.scope
2024-10-18 22:18:29+00:00 [Note] [Entrypoint]: Switching to dedicated user 'mysql'
2024-10-18 22:18:29+00:00 [Note] [Entrypoint]: Entrypoint script for MariaDB Server 1:11.5.2+maria~ubu2404 started.
2024-10-18 22:18:29+00:00 [ERROR] [Entrypoint]: Database is uninitialized and password option is not specified
        You need to specify one of MARIADB_ROOT_PASSWORD, MARIADB_ROOT_PASSWORD_HASH, MARIADB_ALLOW_EMPTY_ROOT_PASSWORD and MARIADB_RANDOM_ROOT_PASSWORD

In the log inspection we found that it is asking to provide one of the environment variable to run the container.

Output


controlplane $ docker run -d --name xander  -e MARIADB_ROOT_PASSWORD=password mariadb       
docker: Error response from daemon: Conflict. The container name "/xander" is already in use by container "dff2bf072092f8a2a19029dee93d99c1fbb8a0274828b8e4c8dbf34195c9597d". You have to remove (or rename) that container to be able to reuse that name.
See 'docker run --help'.

Now there is a conflict because container with same name is already present.

Output


controlplane $ docker rm xander
xander

Try again running the same command and this time it worked!!

Output


controlplane $ docker run -d --name xander -e MARIADB_ROOT_PASSWORD=password mariadb
aa39301ca6be70ed02b2e3ebf34e6b4da7330e1987791ba4c31715676ce5a23d
controlplane $ docker ps -a
CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS         PORTS      NAMES
aa39301ca6be   mariadb   "docker-entrypoint.s…"   6 seconds ago   Up 5 seconds   3306/tcp   xander