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* take a stab at fixing a broken link Signed-off-by: LRubin <lrubin@docker.com> * Update systemd.md Removed the quotes from the --graph option on line 130. Using quotes works for version 1.12 of Docker but with 1.13, Docker will create a directory named <double-quotes> under / and then create a directory of mnt/docker-data" under that directory.
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description, keywords, title
| description | keywords | title |
|---|---|---|
| How to write to and view a container's logs | docker, logging | View a container's logs |
The docker logs command shows information logged by a running container. The
information that is logged and the format of the log depends almost entirely on
the container's endpoint command.
By default, docker logs shows the command's output just as it would appear if
you ran the command interactively in a terminal. UNIX and Linux commands
typically open three I/O streams when they run, called STDIN, STDOUT, and
STDERR. STDIN is the commmand's input stream, which may include input from
the keyboard or input from another command. STDOUT is usually a command's
normal output, and STDERR is typically used to output error messages. By
default, docker logs shows the command's STDOUT and STDERR. To read more
about I/O and Linux, see the
Linux Documentation Project article on I/O redirection
In some cases, docker logs may not show useful information unless you take
additional steps.
-
If you use a logging driver which sends logs to a file, an external host, a database, or another logging back-end,
docker logsmay not show useful information. -
If your image runs a non-interactive process such as a web server or a database, that application may send its output to log files instead of
STDOUTandSTDERR.
In the first case, your logs are processed in other ways and you may choose not
to use docker logs. In the second case, the official nginx image shows one
workaround, and the official Apache httpd image shows another.
The official nginx image creates a symbolic link from
/var/log/nginx/access.log to /dev/stdout, and creates another symbolic link
from /var/log/nginx/error.log to /dev/stderr, overwriting the previous
devices in the process. See the
Dockerfile.
The official httpd driver changes the httpd application's configuration to
write its normal output directly to /proc/self/fd/1 (which is STDOUT) and
its errors to /proc/self/fd/2 (which is STDERR). See the
Dockerfile.
Next steps
- Learn about using custom logging drivers.
- Learn about writing a Dockerfile.