View a container's logs
Estimated reading time: 1 minuteThe 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 logs
may 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
STDOUT
andSTDERR
.
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.