This is the command to check the docker container logs(info level by default) live:
docker logs -f CONTAINER_ID
But what if I want to check the live debug logs which I have logged in my code at debug level?
This is the command to check the docker container logs(info level by
default) live:
docker logs -f CONTAINER_ID
Not really, docker logs CONTAINER_ID doesn't cope with verbosity level.
It simply output the container STDOUT and STDERR.
But what if I want to check the live debug logs which I have logged in
my code at debug level?
That is a very good question.
You could statically (via configuration file) configure your logger appender to write to stdout for all logs (debug and above).
But as side effect, it will log always with that level. For a simple test, it is fine but for a long time running container it may be annoying.
In that case, a dynamic approach to set the logger level is be better (a basic rest controller may very well do the job).
And in that way docker logs -F CONTAINER_ID will output more or less logs according to the current level.
You can run the container in foreground mode so you will able to see log.
docker run -it --rm my_node_app
-it keep the container running in foreground as a result you will able to see your container logs.
You will able to see live logs same like running application in terminal.
But what if I want to check the live debug logs which I have logged in
my code at debug level?
The container output logs totally depend upon the stdout/stderr of the main process that is defined in CMD.
You can filter Debug logs from the log output, as docker does not know the logs format it just print the logs which is available in the form of stdout/stderr.
You can try
docker logs -f container_id | grep "Debug"
If the logs formate contains debug or similar pattern.
Related
I use Dokku to run my app, and for some reason, the container is dying every few hours and recreates itself.
In order to investigate the issue, I am willing to read the error logs to this container and understand why it's crashing. Since Docker clears logs of dead containers, this is impossible.
I turned on docker events and it shows many events (like container update, container kill, container die, etc.) But no sign of what triggered this kill.
How can I investigate the issue?
Versions:
Docker version 19.03.13, build 4484c46d9d
dokku version 0.25.1
Logs are deleted when the container is deleted. If you want the logs to persist, then you need to avoid deleting the container. Make sure you aren't running the container with an option like --rm that automatically deletes it on exit. And check for the obvious issues like running out of disk space.
There are several things you can do to investigate the issue:
You can run the container in the foreground and allow it to log to your console.
If you were previously starting the container in the background with docker run -d (or docker-compose up -d), just remove the -d from the command line and allow the container to log to your terminal. When it crashes, you'll be able to see the most recent logs and scroll back to the limits of your terminal's history buffer.
You can even capture this output to a file using e.g. the script tool:
script -c 'docker run ...`
This will dump all the output to a file named typescript, although you can of course provide a different output name on the command line.
You can change the log driver.
You can configure your container to use a different logging driver. If you select something like syslog or journald, your container logs will be sent to the corrresponding service, and will continue to be available even after the container has been deleted.
I like use the journald logging driver because this allows searching for output by container id. For example, if I start a container like this:
docker run --log-driver journald --name web -p 8080:8080 -d docker.io/alpinelinux/darkhttpd
I can see logs from that container by running:
$ journalctl CONTAINER_NAME=web
Feb 25 20:50:04 docker 0bff1aec9b65[660]: darkhttpd/1.13, copyright (c) 2003-2021 Emil Mikulic.
These logs will persist even after the container exits.
(You can also search by container id instead of name by using CONTAINER_ID_FULL (the full id) or CONTAINER_ID (the short id), or even by image name with IMAGE_NAME.)
I have a simple code for which I have created a docker container and the status shows it running fine. Inside the code I have used some print() commands to print the data. I wanted to see that print command output.
For this I have seen docker logs . But it seems not to be working as it shows no logs. How to check logs.?
$ sudo docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a3b3fd261b94 myfirstdocker "python3 ./my_script…" 22 minutes ago Up 22 minutes elegant_darwin
$ sudo docker logs a3b3fd261b94
<shows nothing>
The first point you need to print your logs to stdout.
To check docker logs just use the following command:
docker logs --help
Usage: docker logs [OPTIONS] CONTAINER
Fetch the logs of a container
Options:
--details Show extra details provided to logs
-f, --follow Follow log output
--help Print usage
--since string Show logs since timestamp
--tail string Number of lines to show from the end of the logs (default "all")
-t, --timestamps Show timestamps
Some example:
docker logs --since=1h <container_id>
4
Let's try using that docker create start and then logs command again and see what happens.
sudo docker create busybox echo hi there
output of the command
now I will take the ID and run a docker start and paste the ID that starts up the container it executes echo high there inside of it and then immediately exits.
Now I want to go back to that stopped container and get all the logs that have been emitted inside of it.
To do so I can run at docker logs and then paste the ID in and I will see that when the container had been running it had printed out the string Hi there.
One thing to be really clear about is that by running docker logs I am not re-running or restarting the container to in any way shape or form, I am just getting a record of all the logs that have been emitted from that container.
docker logs container_id
If there's not so much supposed output (e.g. script just tries to print few bytes), I'd suspect python is buffering it.
Try adding more data to the output to be sure that buffer is flushed, and also using PYTHONUNBUFFERED=1 (although, python3 still may do some buffering despite of this setting).
My Docker container produces multiple application logs.
docker logs command only shows the app startup logs. Is there a way to redirect the other log files so they are shown by the docker logs command?
EDIT:
I'm using the WebSphere traditional docker image. Docker logs only shows the startServer.log but there are other logs like SystemOut.log ....
We need more information, like which application, your Dockerfile, etc.
As a general answer you must have an entry point script which will send your application log to stdout:
runapp &
tail -f logfile
Something like that.
Regards
docker logs will display all the stdout and stderr from the application running in the container. Configure the application to log to stderr instead of a log file and the logs will be visible from docker logs.
I currently use docker for my backend, and when I first start them up with
docker-compose up
I get log outputs of all 4 dockers at once, so I can see how they are interacting with each other when a request comes in. Looking like this, one request going from nginx to couchdb
The issue is now that I am running on GCE with load balancing, when a new VM spins up, it auto starts the dockers and runs normally, I would like to be able to access a load balanced VM and view the live logs, but I can not get docker to allow me this style, when I use logs, it gives me normal all white font with no label of where it came from.
Using
docker events
does nothing, it won't return any info.
tldr; what is the best way to obtain a view, same as the log output you get when running "docker-compose up"
If using docker-compose, you use
docker-compose logs --tail=0 --follow
instead of
docker logs --tail=0 --follow
This will get the output I was originally looking for.
You can see the logs for all running containers with
docker ps -q | xargs -L 1 docker logs
In theory this might work for the --follow too if xargs is ran with -P <count>, where the count is higher than the number of running containers.
I use a variation of this to live tail (--follow) all logs and indicate which log is tailing at the time. This bash includes both stdout and stderr. Note you may need to purge the /tmp dir of *.{log,err} afterwards.
for c in $(docker ps -a --format="{{.Names}}")
do
docker logs -f $c > /tmp/$c.log 2> /tmp/$c.err &
done
tail -f /tmp/*.{log,err}
Hope this helps. Logging has become so problematic these days, and other get-off-my-lawn old man rants...
Try "watch"
Here's a quick and dirty multitail/xtail for docker containers.
watch 'docker ps --format "{{.Names}}" | sort | xargs --verbose --max-args=1 -- docker logs --tail=8 --timestamps'
How this works:
watch to run every few seconds
docker ps --format "{{.Names}}" to get the names of all running containers
sort to sort them
xargs to give these names to docker logs:
docker logs to print the actual logs
Adjust parameter "--tail=8" as needed so that everything still fits on one screen.
The "xargs" methods listed above (in another user's answer) will stop working as containers are stopped and restarted. This "watch" method here does not have that problem. (But it's not great either.)
If you are using Docker Swarm, you can find your services by
docker service ls
Grap the id, and then run
docker service logs $ID -f
if the service is defined with tty: true, then you must run with the --raw flag. Notice, this wont tell you which container is giving the outputted log entry.
When I start my docker daemon with service docker start or docker -d, I usually get my shell terminal. But when there's docker daemon log need to be output, log is printed directly on my screen and I lost my shell terminal. I press ENTER and get shell terminal again. I don't want this. Printing docker daemon log into log files will be better to me. How to print my docker log into logfiles rather than STDOUT?
Unix has a concept of 'redirection', so you can ask stdout to go to a file instead using a command like this:
docker -d > my_logfile
(you would probably also want to redirect stderr)
Now,a more complicated version of this is exactly what the docker service startup script does:
start-stop-daemon [...] >> "$DOCKER_LOGFILE" 2>&1
so I'm not sure why you are seeing output to your terminal if you use that route.