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55 lines
2.7 KiB
Markdown
55 lines
2.7 KiB
Markdown
---
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description: How to write to and view a container's logs
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keywords: docker, logging
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title: View logs for a container or service
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redirect_from:
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- /engine/admin/logging/
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- /engine/admin/logging/view_container_logs/
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---
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The `docker logs` command shows information logged by a running container. The
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`docker service logs` command shows information logged by all containers
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participating in a service. The information that is logged and the format of the
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log depends almost entirely on the container's endpoint command.
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By default, `docker logs` or `docker service logs` shows the command's output
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just as it would appear if you ran the command interactively in a terminal. UNIX
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and Linux commands typically open three I/O streams when they run, called
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`STDIN`, `STDOUT`, and `STDERR`. `STDIN` is the commmand's input stream, which
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may include input from the keyboard or input from another command. `STDOUT` is
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usually a command's normal output, and `STDERR` is typically used to output
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error messages. By default, `docker logs` shows the command's `STDOUT` and
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`STDERR`. To read more about I/O and Linux, see the
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[Linux Documentation Project article on I/O redirection](http://www.tldp.org/LDP/abs/html/io-redirection.html).
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In some cases, `docker logs` may not show useful information unless you take
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additional steps.
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- If you use a [logging driver](configure.md) which sends logs to a file, an
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external host, a database, or another logging back-end, `docker logs` may not
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show useful information.
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- If your image runs a non-interactive process such as a web server or a
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database, that application may send its output to log files instead of `STDOUT`
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and `STDERR`.
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In the first case, your logs are processed in other ways and you may choose not
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to use `docker logs`. In the second case, the official `nginx` image shows one
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workaround, and the official Apache `httpd` image shows another.
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The official `nginx` image creates a symbolic link from
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`/dev/stdout` to `/var/log/nginx/access.log`, and creates another symbolic link
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from `/dev/stderr` to `/var/log/nginx/error.log`, overwriting the log files and
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causing logs to be sent to the relevant special device instead. See the
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[Dockerfile](https://github.com/nginxinc/docker-nginx/blob/8921999083def7ba43a06fabd5f80e4406651353/mainline/jessie/Dockerfile#L21-L23).
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The official `httpd` driver changes the `httpd` application's configuration to
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write its normal output directly to `/proc/self/fd/1` (which is `STDOUT`) and
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its errors to `/proc/self/fd/2` (which is `STDERR`). See the
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[Dockerfile](https://github.com/docker-library/httpd/blob/b13054c7de5c74bbaa6d595dbe38969e6d4f860c/2.2/Dockerfile#L72-L75).
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## Next steps
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- Configure [logging drivers](configure.md).
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- Write a [Dockerfile](/engine/reference/builder.md).
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