View logs for a container or service
Estimated reading time: 2 minutesThe docker logs
command shows information logged by a running container. The
docker service logs
command shows information logged by all containers
participating in a service. The information that is logged and the format of the
log depends almost entirely on the container’s endpoint command.
By default, docker logs
or docker service 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 command’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 log files and
causing logs to be sent to the relevant special device instead. 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
- Configure logging drivers.
- Write a Dockerfile.