docker run
DOCKER(1) JUNE 2014 DOCKER(1)
NAME
docker-run - Run a command in a new container
SYNOPSIS
docker run [-a|--attach[=[]]] [--add-host[=[]]]
[--blkio-weight[=[BLKIO-WEIGHT]]] [--blkio-weight-device[=[]]]
[--cpu-shares[=0]] [--cap-add[=[]]] [--cap-drop[=[]]] [--cgroup-par-
ent[=CGROUP-PATH]] [--cidfile[=CIDFILE]] [--cpu-period[=0]]
[--cpu-quota[=0]] [--cpuset-cpus[=CPUSET-CPUS]]
[--cpuset-mems[=CPUSET-MEMS]] [-d|--detach] [--detach-keys[=[]]]
[--device[=[]]] [--device-read-bps[=[]]] [--device-read-iops[=[]]]
[--device-write-bps[=[]]] [--device-write-iops[=[]]] [--dns[=[]]]
[--dns-opt[=[]]] [--dns-search[=[]]] [-e|--env[=[]]] [--entry-
point[=ENTRYPOINT]] [--env-file[=[]]] [--expose[=[]]]
[--group-add[=[]]] [-h|--hostname[=HOSTNAME]] [--help] [-i|--interac-
tive] [--ip[=IPv4-ADDRESS]] [--ip6[=IPv6-ADDRESS]] [--ipc[=IPC]]
[--isolation[=default]] [--kernel-memory[=KERNEL-MEMORY]]
[-l|--label[=[]]] [--label-file[=[]]] [--link[=[]]] [--log-driver[=[]]]
[--log-opt[=[]]] [-m|--memory[=MEMORY]] [--mac-address[=MAC-ADDRESS]]
[--memory-reservation[=MEMORY-RESERVATION]] [--memory-swap[=LIMIT]]
[--memory-swappiness[=MEMORY-SWAPPINESS]] [--name[=NAME]]
[--net[="bridge"]] [--net-alias[=[]]] [--oom-kill-disable]
[--oom-score-adj[=0]] [-P|--publish-all] [-p|--publish[=[]]]
[--pid[=[]]] [--userns[=[]]] [--pids-limit[=PIDS_LIMIT]] [--privileged]
[--read-only] [--restart[=RESTART]] [--rm] [--security-opt[=[]]]
[--stop-signal[=SIGNAL]] [--shm-size[=[]]] [--sig-proxy[=true]]
[-t|--tty] [--tmpfs[=[CONTAINER-DIR[:<OPTIONS>]]] [-u|--user[=USER]]
[--ulimit[=[]]] [--uts[=[]]] [-v|--volume[=[[HOST-DIR:]CON-
TAINER-DIR[:OPTIONS]]]] [--volume-driver[=DRIVER]] [--vol-
umes-from[=[]]] [-w|--workdir[=WORKDIR]] IMAGE [COMMAND] [ARG...]
DESCRIPTION
Run a process in a new container. docker run starts a process with its
own file system, its own networking, and its own isolated process tree.
The IMAGE which starts the process may define defaults related to the
process that will be run in the container, the networking to expose,
and more, but docker run gives final control to the operator or admin-
istrator who starts the container from the image. For that reason
docker run has more options than any other Docker command.
If the IMAGE is not already loaded then docker run will pull the IMAGE,
and all image dependencies, from the repository in the same way running
docker pull IMAGE, before it starts the container from that image.
OPTIONS
-a, --attach=[]
Attach to STDIN, STDOUT or STDERR.
In foreground mode (the default when -d is not specified), docker run
can start the process in the container and attach the console to the
process's standard input, output, and standard error. It can even pre-
tend to be a TTY (this is what most commandline executables expect) and
pass along signals. The -a option can be set for each of stdin, stdout,
and stderr.
--add-host=[]
Add a custom host-to-IP mapping (host:ip)
Add a line to /etc/hosts. The format is hostname:ip. The --add-host
option can be set multiple times.
--blkio-weight=0
Block IO weight (relative weight) accepts a weight value between 10
and 1000.
--blkio-weight-device=[]
Block IO weight (relative device weight, format:
DEVICE_NAME:WEIGHT).
--cpu-shares=0
CPU shares (relative weight)
By default, all containers get the same proportion of CPU cycles. This
proportion can be modified by changing the container's CPU share
weighting relative to the weighting of all other running containers.
To modify the proportion from the default of 1024, use the --cpu-shares
flag to set the weighting to 2 or higher.
The proportion will only apply when CPU-intensive processes are run-
ning. When tasks in one container are idle, other containers can use
the left-over CPU time. The actual amount of CPU time will vary depend-
ing on the number of containers running on the system.
For example, consider three containers, one has a cpu-share of 1024 and
two others have a cpu-share setting of 512. When processes in all three
containers attempt to use 100% of CPU, the first container would
receive 50% of the total CPU time. If you add a fourth container with a
cpu-share of 1024, the first container only gets 33% of the CPU. The
remaining containers receive 16.5%, 16.5% and 33% of the CPU.
On a multi-core system, the shares of CPU time are distributed over all
CPU cores. Even if a container is limited to less than 100% of CPU
time, it can use 100% of each individual CPU core.
For example, consider a system with more than three cores. If you start
one container {C0} with -c=512 running one process, and another con-
tainer {C1} with -c=1024 running two processes, this can result in the
following division of CPU shares:
PID container CPU CPU share
100 {C0} 0 100% of CPU0
101 {C1} 1 100% of CPU1
102 {C1} 2 100% of CPU2
--cap-add=[]
Add Linux capabilities
--cap-drop=[]
Drop Linux capabilities
--cgroup-parent=""
Path to cgroups under which the cgroup for the container will be
created. If the path is not absolute, the path is considered to be rel-
ative to the cgroups path of the init process. Cgroups will be created
if they do not already exist.
--cidfile=""
Write the container ID to the file
--cpu-period=0
Limit the CPU CFS (Completely Fair Scheduler) period
Limit the container's CPU usage. This flag tell the kernel to restrict
the container's CPU usage to the period you specify.
--cpuset-cpus=""
CPUs in which to allow execution (0-3, 0,1)
--cpuset-mems=""
Memory nodes (MEMs) in which to allow execution (0-3, 0,1). Only
effective on NUMA systems.
If you have four memory nodes on your system (0-3), use
--cpuset-mems=0,1 then processes in your Docker container will only use
memory from the first two memory nodes.
--cpu-quota=0
Limit the CPU CFS (Completely Fair Scheduler) quota
Limit the container's CPU usage. By default, containers run with the
full CPU resource. This flag tell the kernel to restrict the con-
tainer's CPU usage to the quota you specify.
-d, --detach=true|false
Detached mode: run the container in the background and print the new
container ID. The default is false.
At any time you can run docker ps in the other shell to view a list of
the running containers. You can reattach to a detached container with
docker attach. If you choose to run a container in the detached mode,
then you cannot use the -rm option.
When attached in the tty mode, you can detach from the container (and
leave it running) using a configurable key sequence. The default
sequence is CTRL-p CTRL-q. You configure the key sequence using the
--detach-keys option or a configuration file. See config-json(5) for
documentation on using a configuration file.
--detach-keys=""
Override the key sequence for detaching a container. Format is a
single character [a-Z] or ctrl-<value> where <value> is one of: a-z, @,
^, [, , or _.
--device=[]
Add a host device to the container (e.g.
--device=/dev/sdc:/dev/xvdc:rwm)
--device-read-bps=[]
Limit read rate from a device (e.g. --device-read-bps=/dev/sda:1mb)
--device-read-iops=[]
Limit read rate from a device (e.g.
--device-read-iops=/dev/sda:1000)
--device-write-bps=[]
Limit write rate to a device (e.g. --device-write-bps=/dev/sda:1mb)
--device-write-iops=[]
Limit write rate a a device (e.g. --device-write-iops=/dev/sda:1000)
--dns-search=[]
Set custom DNS search domains (Use --dns-search=. if you don't wish
to set the search domain)
--dns-opt=[]
Set custom DNS options
--dns=[]
Set custom DNS servers
This option can be used to override the DNS configuration passed to the
container. Typically this is necessary when the host DNS configuration
is invalid for the container (e.g., 127.0.0.1). When this is the case
the --dns flags is necessary for every run.
-e, --env=[]
Set environment variables
This option allows you to specify arbitrary environment variables that
are available for the process that will be launched inside of the con-
tainer.
--entrypoint=""
Overwrite the default ENTRYPOINT of the image
This option allows you to overwrite the default entrypoint of the image
that is set in the Dockerfile. The ENTRYPOINT of an image is similar to
a COMMAND because it specifies what executable to run when the con-
tainer starts, but it is (purposely) more difficult to override. The
ENTRYPOINT gives a container its default nature or behavior, so that
when you set an ENTRYPOINT you can run the container as if it were that
binary, complete with default options, and you can pass in more options
via the COMMAND. But, sometimes an operator may want to run something
else inside the container, so you can override the default ENTRYPOINT
at runtime by using a --entrypoint and a string to specify the new
ENTRYPOINT.
--env-file=[]
Read in a line delimited file of environment variables
--expose=[]
Expose a port, or a range of ports (e.g. --expose=3300-3310) informs
Docker that the container listens on the specified network ports at
runtime. Docker uses this information to interconnect containers using
links and to set up port redirection on the host system.
--group-add=[]
Add additional groups to run as
-h, --hostname=""
Container host name
Sets the container host name that is available inside the container.
--help
Print usage statement
-i, --interactive=true|false
Keep STDIN open even if not attached. The default is false.
When set to true, keep stdin open even if not attached. The default is
false.
--ip=""
Sets the container's interface IPv4 address (e.g. 172.23.0.9)
It can only be used in conjunction with --net for user-defined networks
--ip6=""
Sets the container's interface IPv6 address (e.g. 2001:db8::1b99)
It can only be used in conjunction with --net for user-defined networks
--ipc=""
Default is to create a private IPC namespace (POSIX SysV IPC) for
the container
'container:<name|id>': reuses another
container shared memory, semaphores and message queues
'host': use the host shared memory,sema-
phores and message queues inside the container. Note: the host mode
gives the container full access to local shared memory and is therefore
considered insecure.
--isolation="default"
Isolation specifies the type of isolation technology used by con-
tainers.
-l, --label=[]
Set metadata on the container (e.g., --label com.example.key=value)
--kernel-memory=""
Kernel memory limit (format: <number>[<unit>], where unit = b, k, m
or g)
Constrains the kernel memory available to a container. If a limit of 0
is specified (not using --kernel-memory), the container's kernel memory
is not limited. If you specify a limit, it may be rounded up to a mul-
tiple of the operating system's page size and the value can be very
large, millions of trillions.
--label-file=[]
Read in a line delimited file of labels
--link=[]
Add link to another container in the form of <name or id>:alias or
just <name or id> in which case the alias will match the name
If the operator uses --link when starting the new client container,
then the client container can access the exposed port via a private
networking interface. Docker will set some environment variables in the
client container to help indicate which interface and port to use.
--log-driver="json-file|syslog|journald|gelf|flu-
entd|awslogs|splunk|etwlogs|gcplogs|none"
Logging driver for container. Default is defined by daemon
--log-driver flag.
Warning: the docker logs command works only for the json-file and
journald logging drivers.
--log-opt=[]
Logging driver specific options.
-m, --memory=""
Memory limit (format: <number>[<unit>], where unit = b, k, m or g)
Allows you to constrain the memory available to a container. If the
host supports swap memory, then the -m memory setting can be larger
than physical RAM. If a limit of 0 is specified (not using -m), the
container's memory is not limited. The actual limit may be rounded up
to a multiple of the operating system's page size (the value would be
very large, that's millions of trillions).
--memory-reservation=""
Memory soft limit (format: <number>[<unit>], where unit = b, k, m or
g)
After setting memory reservation, when the system detects memory con-
tention or low memory, containers are forced to restrict their consump-
tion to their reservation. So you should always set the value below
--memory, otherwise the hard limit will take precedence. By default,
memory reservation will be the same as memory limit.
--memory-swap="LIMIT"
A limit value equal to memory plus swap. Must be used with the -m
(--memory) flag. The swap LIMIT should always be larger than -m (--mem-
ory) value.
The format of LIMIT is <number>[<unit>]. Unit can be b (bytes), k
(kilobytes), m (megabytes), or g (gigabytes). If you don't specify a
unit, b is used. Set LIMIT to -1 to enable unlimited swap.
--mac-address=""
Container MAC address (e.g. 92:d0:c6:0a:29:33)
Remember that the MAC address in an Ethernet network must be unique.
The IPv6 link-local address will be based on the device's MAC address
according to RFC4862.
--name=""
Assign a name to the container
The operator can identify a container in three ways:
UUID long identifier
("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778")
UUID short identifier ("f78375b1c487")
Name ("jonah")
The UUID identifiers come from the Docker daemon, and if a name is not
assigned to the container with --name then the daemon will also gener-
ate a random string name. The name is useful when defining links (see
--link) (or any other place you need to identify a container). This
works for both background and foreground Docker containers.
--net="bridge"
Set the Network mode for the container
'bridge': create a network stack on the
default Docker bridge
'none': no networking
'container:<name|id>': reuse another
container's network stack
'host': use the Docker host network
stack. Note: the host mode gives the container full access to local
system services such as D-bus and is therefore considered insecure.
'<network-name>|<network-id>': connect
to a user-defined network
--net-alias=[]
Add network-scoped alias for the container
--oom-kill-disable=true|false
Whether to disable OOM Killer for the container or not.
--oom-score-adj=""
Tune the host's OOM preferences for containers (accepts -1000 to
1000)
-P, --publish-all=true|false
Publish all exposed ports to random ports on the host interfaces.
The default is false.
When set to true publish all exposed ports to the host interfaces. The
default is false. If the operator uses -P (or -p) then Docker will make
the exposed port accessible on the host and the ports will be available
to any client that can reach the host. When using -P, Docker will bind
any exposed port to a random port on the host within an ephemeral port
range defined by /proc/sys/net/ipv4/ip_local_port_range. To find the
mapping between the host ports and the exposed ports, use docker port.
-p, --publish=[]
Publish a container's port, or range of ports, to the host.
Format: ip:hostPort:containerPort | ip::containerPort | hostPort:con-
tainerPort | containerPort Both hostPort and containerPort can be spec-
ified as a range of ports. When specifying ranges for both, the number
of container ports in the range must match the number of host ports in
the range. (e.g., docker run -p 1234-1236:1222-1224 --name thisWorks
-t busybox but not docker run -p 1230-1236:1230-1240 --name RangeCon-
tainerPortsBiggerThanRangeHostPorts -t busybox) With ip: docker run -p
127.0.0.1:$HOSTPORT:$CONTAINERPORT --name CONTAINER -t someimage Use
docker port to see the actual mapping: docker port CONTAINER $CONTAIN-
ERPORT
--pid=host
Set the PID mode for the container
host: use the host's PID namespace inside the container.
Note: the host mode gives the container full access to local PID
and is therefore considered insecure.
--userns=""
Set the usernamespace mode for the container when userns-remap
option is enabled.
host: use the host usernamespace and enable all privileged options
(e.g., pid=host or --privileged).
--pids-limit=""
Tune the container's pids limit. Set -1 to have unlimited pids for
the container.
--uts=host
Set the UTS mode for the container
host: use the host's UTS namespace inside the container.
Note: the host mode gives the container access to changing the
host's hostname and is therefore considered insecure.
--privileged=true|false
Give extended privileges to this container. The default is false.
By default, Docker containers are "unprivileged" (=false) and cannot,
for example, run a Docker daemon inside the Docker container. This is
because by default a container is not allowed to access any devices. A
"privileged" container is given access to all devices.
When the operator executes docker run --privileged, Docker will enable
access to all devices on the host as well as set some configuration in
AppArmor to allow the container nearly all the same access to the host
as processes running outside of a container on the host.
--read-only=true|false
Mount the container's root filesystem as read only.
By default a container will have its root filesystem writable allowing
processes to write files anywhere. By specifying the --read-only flag
the container will have its root filesystem mounted as read only pro-
hibiting any writes.
--restart="no"
Restart policy to apply when a container exits (no, on-fail-
ure[:max-retry], always, unless-stopped).
--rm=true|false
Automatically remove the container when it exits (incompatible with
-d). The default is false.
--security-opt=[]
Security Options
"label=user:USER" : Set the label user for the container
"label=role:ROLE" : Set the label role for the container
"label=type:TYPE" : Set the label type for the container
"label=level:LEVEL" : Set the label level for the container
"label=disable" : Turn off label confinement for the container
"no-new-privileges" : Disable container processes from gaining additional privileges
"seccomp=unconfined" : Turn off seccomp confinement for the container
"seccomp=profile.json : White listed syscalls seccomp Json file to be used as a seccomp filter
"apparmor=unconfined" : Turn off apparmor confinement for the container
"apparmor=your-profile" : Set the apparmor confinement profile for the container
--stop-signal=SIGTERM
Signal to stop a container. Default is SIGTERM.
--shm-size=""
Size of /dev/shm. The format is <number><unit>.
number must be greater than 0. Unit is optional and can be b
(bytes), k (kilobytes), m(megabytes), or g (gigabytes).
If you omit the unit, the system uses bytes. If you omit the size
entirely, the system uses 64m.
--sig-proxy=true|false
Proxy received signals to the process (non-TTY mode only). SIGCHLD,
SIGSTOP, and SIGKILL are not proxied. The default is true.
--memory-swappiness=""
Tune a container's memory swappiness behavior. Accepts an integer
between 0 and 100.
-t, --tty=true|false
Allocate a pseudo-TTY. The default is false.
When set to true Docker can allocate a pseudo-tty and attach to the
standard input of any container. This can be used, for example, to run
a throwaway interactive shell. The default is false.
The -t option is incompatible with a redirection of the docker client
standard input.
--tmpfs=[] Create a tmpfs mount
Mount a temporary filesystem (tmpfs) mount into a container, for exam-
ple:
$ docker run -d --tmpfs /tmp:rw,size=787448k,mode=1777 my_image
This command mounts a tmpfs at /tmp within the container. The sup-
ported mount options are the same as the Linux default mount flags. If
you do not specify any options, the systems uses the following options:
rw,noexec,nosuid,nodev,size=65536k.
-u, --user=""
Sets the username or UID used and optionally the groupname or GID
for the specified command.
The followings examples are all valid:
--user [user | user:group | uid | uid:gid | user:gid | uid:group ]
Without this argument the command will be run as root in the container.
--ulimit=[]
Ulimit options
-v|--volume[=[[HOST-DIR:]CONTAINER-DIR[:OPTIONS]]]
Create a bind mount. If you specify, -v /HOST-DIR:/CONTAINER-DIR,
Docker
bind mounts /HOST-DIR in the host to /CONTAINER-DIR in the Docker
container. If 'HOST-DIR' is omitted, Docker automatically creates
the new
volume on the host. The OPTIONS are a comma delimited list and can
be:
0
item [rw|ro] item [z|Z] item [[r]shared|[r]slave|[r]private]
item [nocopy]
The CONTAINER-DIR must be an absolute path such as /src/docs. The
HOST-DIR can be an absolute path or a name value. A name value must
start with an alphanumeric character, followed by a-z0-9, _ (under-
score), . (period) or - (hyphen). An absolute path starts with a /
(forward slash).
If you supply a HOST-DIR that is an absolute path, Docker bind-mounts
to the path you specify. If you supply a name, Docker creates a named
volume by that name. For example, you can specify either /foo or foo
for a HOST-DIR value. If you supply the /foo value, Docker creates a
bind-mount. If you supply the foo specification, Docker creates a named
volume.
You can specify multiple -v options to mount one or more mounts to a
container. To use these same mounts in other containers, specify the
--volumes-from option also.
You can add :ro or :rw suffix to a volume to mount it read-only or
read-write mode, respectively. By default, the volumes are mounted
read-write. See examples.
Labeling systems like SELinux require that proper labels are placed on
volume content mounted into a container. Without a label, the security
system might prevent the processes running inside the container from
using the content. By default, Docker does not change the labels set by
the OS.
To change a label in the container context, you can add either of two
suffixes :z or :Z to the volume mount. These suffixes tell Docker to
relabel file objects on the shared volumes. The z option tells Docker
that two containers share the volume content. As a result, Docker
labels the content with a shared content label. Shared volume labels
allow all containers to read/write content. The Z option tells Docker
to label the content with a private unshared label. Only the current
container can use a private volume.
By default bind mounted volumes are private. That means any mounts done
inside container will not be visible on host and vice-a-versa. One can
change this behavior by specifying a volume mount propagation property.
Making a volume shared mounts done under that volume inside container
will be visible on host and vice-a-versa. Making a volume slave enables
only one way mount propagation and that is mounts done on host under
that volume will be visible inside container but not the other way
around.
To control mount propagation property of volume one can use :[r]shared,
:[r]slave or :[r]private propagation flag. Propagation property can be
specified only for bind mounted volumes and not for internal volumes or
named volumes. For mount propagation to work source mount point (mount
point where source dir is mounted on) has to have right propagation
properties. For shared volumes, source mount point has to be shared.
And for slave volumes, source mount has to be either shared or slave.
Use df <source-dir> to figure out the source mount and then use findmnt
-o TARGET,PROPAGATION <source-mount-dir> to figure out propagation
properties of source mount. If findmnt utility is not available, then
one can look at mount entry for source mount point in
/proc/self/mountinfo. Look at optional fields and see if any propagaion
properties are specified. shared:X means mount is shared, master:X
means mount is slave and if nothing is there that means mount is pri-
vate.
To change propagation properties of a mount point use mount command.
For example, if one wants to bind mount source directory /foo one can
do mount --bind /foo /foo and mount --make-private --make-shared /foo.
This will convert /foo into a shared mount point. Alternatively one can
directly change propagation properties of source mount. Say / is source
mount for /foo, then use mount --make-shared / to convert / into a
shared mount.
Note: When using systemd to manage the Docker daemon's start and
stop, in the systemd unit file there is an option to control
mount propagation for the Docker daemon itself, called Mount-
Flags. The value of this setting may cause Docker to not see
mount propagation changes made on the mount point. For example,
if this value is slave, you may not be able to use the shared or
rshared propagation on a volume.
To disable automatic copying of data from the container path to the
volume, use the nocopy flag. The nocopy flag can be set on bind mounts
and named volumes.
--volume-driver=""
Container's volume driver. This driver creates volumes specified
either from
a Dockerfile's VOLUME instruction or from the docker run -v flag.
See docker-volume-create(1) for full details.
--volumes-from=[]
Mount volumes from the specified container(s)
Mounts already mounted volumes from a source container onto another
container. You must supply the source's container-id. To share
a volume, use the --volumes-from option when running
the target container. You can share volumes even if the source con-
tainer
is not running.
By default, Docker mounts the volumes in the same mode (read-write or
read-only) as it is mounted in the source container. Optionally, you
can change this by suffixing the container-id with either the :ro or
:rw keyword.
If the location of the volume from the source container overlaps with
data residing on a target container, then the volume hides
that data on the target.
-w, --workdir=""
Working directory inside the container
The default working directory for running binaries within a container
is the root directory (/). The developer can set a different default
with the Dockerfile WORKDIR instruction. The operator can override the
working directory by using the -w option.
Exit Status
The exit code from docker run gives information about why the container
failed to run or why it exited. When docker run exits with a non-zero
code, the exit codes follow the chroot standard, see below:
125 if the error is with Docker daemon itself
$ docker run --foo busybox; echo $?
# flag provided but not defined: --foo
See 'docker run --help'.
125
126 if the contained command cannot be invoked
$ docker run busybox /etc; echo $?
# exec: "/etc": permission denied
docker: Error response from daemon: Contained command could not be invoked
126
127 if the contained command cannot be found
$ docker run busybox foo; echo $?
# exec: "foo": executable file not found in $PATH
docker: Error response from daemon: Contained command not found or does not exist
127
Exit code of contained command otherwise
$ docker run busybox /bin/sh -c 'exit 3'
# 3
EXAMPLES
Running container in read-only mode
During container image development, containers often need to write to
the image content. Installing packages into /usr, for example. In
production, applications seldom need to write to the image. Container
applications write to volumes if they need to write to file systems at
all. Applications can be made more secure by running them in read-only
mode using the --read-only switch. This protects the containers image
from modification. Read only containers may still need to write tempo-
rary data. The best way to handle this is to mount tmpfs directories
on /run and /tmp.
# docker run --read-only --tmpfs /run --tmpfs /tmp -i -t fedora /bin/bash
Exposing log messages from the container to the host's log
If you want messages that are logged in your container to show up in
the host's syslog/journal then you should bind mount the /dev/log
directory as follows.
# docker run -v /dev/log:/dev/log -i -t fedora /bin/bash
From inside the container you can test this by sending a message to the
log.
(bash)# logger "Hello from my container"
Then exit and check the journal.
# exit
# journalctl -b | grep Hello
This should list the message sent to logger.
Attaching to one or more from STDIN, STDOUT, STDERR
If you do not specify -a then Docker will attach everything (stdin,std-
out,stderr) you'd like to connect instead, as in:
# docker run -a stdin -a stdout -i -t fedora /bin/bash
Sharing IPC between containers
Using shm_server.c available here:
<https://www.cs.cf.ac.uk/Dave/C/node27.html>
Testing --ipc=host mode:
Host shows a shared memory segment with 7 pids attached, happens to be
from httpd:
$ sudo ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x01128e25 0 root 600 1000 7
Now run a regular container, and it correctly does NOT see the shared
memory segment from the host:
$ docker run -it shm ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
Run a container with the new --ipc=host option, and it now sees the
shared memory segment from the host httpd:
$ docker run -it --ipc=host shm ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x01128e25 0 root 600 1000 7
Testing --ipc=container:CONTAINERID mode:
Start a container with a program to create a shared memory segment:
$ docker run -it shm bash
$ sudo shm/shm_server
$ sudo ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0000162e 0 root 666 27 1
Create a 2nd container correctly shows no shared memory segment from
1st container:
$ docker run shm ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
Create a 3rd container using the new --ipc=container:CONTAINERID
option, now it shows the shared memory segment from the first:
$ docker run -it --ipc=container:ed735b2264ac shm ipcs -m
$ sudo ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0000162e 0 root 666 27 1
Linking Containers
Note: This section describes linking between containers on the
default (bridge) network, also known as "legacy links". Using
--link on user-defined networks uses the DNS-based discovery,
which does not add entries to /etc/hosts, and does not set envi-
ronment variables for discovery.
The link feature allows multiple containers to communicate with each
other. For example, a container whose Dockerfile has exposed port 80
can be run and named as follows:
# docker run --name=link-test -d -i -t fedora/httpd
A second container, in this case called linker, can communicate with
the httpd container, named link-test, by running with the
--link=<name>:<alias>
# docker run -t -i --link=link-test:lt --name=linker fedora /bin/bash
Now the container linker is linked to container link-test with the
alias lt. Running the env command in the linker container shows envi-
ronment variables
with the LT (alias) context (LT_)
# env
HOSTNAME=668231cb0978
TERM=xterm
LT_PORT_80_TCP=tcp://172.17.0.3:80
LT_PORT_80_TCP_PORT=80
LT_PORT_80_TCP_PROTO=tcp
LT_PORT=tcp://172.17.0.3:80
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/
LT_NAME=/linker/lt
SHLVL=1
HOME=/
LT_PORT_80_TCP_ADDR=172.17.0.3
_=/usr/bin/env
When linking two containers Docker will use the exposed ports of the
container to create a secure tunnel for the parent to access.
If a container is connected to the default bridge network and linked
with other containers, then the container's /etc/hosts file is updated
with the linked container's name.
Note Since Docker may live update the container's /etc/hosts
file, there may be situations when processes inside the con-
tainer can end up reading an empty or incomplete /etc/hosts
file. In most cases, retrying the read again should fix the
problem.
Mapping Ports for External Usage
The exposed port of an application can be mapped to a host port using
the -p flag. For example, a httpd port 80 can be mapped to the host
port 8080 using the following:
# docker run -p 8080:80 -d -i -t fedora/httpd
Creating and Mounting a Data Volume Container
Many applications require the sharing of persistent data across several
containers. Docker allows you to create a Data Volume Container that
other containers can mount from. For example, create a named container
that contains directories /var/volume1 and /tmp/volume2. The image will
need to contain these directories so a couple of RUN mkdir instructions
might be required for you fedora-data image:
# docker run --name=data -v /var/volume1 -v /tmp/volume2 -i -t fedora-data true
# docker run --volumes-from=data --name=fedora-container1 -i -t fedora bash
Multiple --volumes-from parameters will bring together multiple data
volumes from multiple containers. And it's possible to mount the vol-
umes that came from the DATA container in yet another container via the
fedora-container1 intermediary container, allowing to abstract the
actual data source from users of that data:
# docker run --volumes-from=fedora-container1 --name=fedora-container2 -i -t fedora bash
Mounting External Volumes
To mount a host directory as a container volume, specify the absolute
path to the directory and the absolute path for the container directory
separated by a colon:
# docker run -v /var/db:/data1 -i -t fedora bash
When using SELinux, be aware that the host has no knowledge of con-
tainer SELinux policy. Therefore, in the above example, if SELinux pol-
icy is enforced, the /var/db directory is not writable to the con-
tainer. A "Permission Denied" message will occur and an avc: message in
the host's syslog.
To work around this, at time of writing this man page, the following
command needs to be run in order for the proper SELinux policy type
label to be attached to the host directory:
# chcon -Rt svirt_sandbox_file_t /var/db
Now, writing to the /data1 volume in the container will be allowed and
the changes will also be reflected on the host in /var/db.
Using alternative security labeling
You can override the default labeling scheme for each container by
specifying the --security-opt flag. For example, you can specify the
MCS/MLS level, a requirement for MLS systems. Specifying the level in
the following command allows you to share the same content between con-
tainers.
# docker run --security-opt label=level:s0:c100,c200 -i -t fedora bash
An MLS example might be:
# docker run --security-opt label=level:TopSecret -i -t rhel7 bash
To disable the security labeling for this container versus running with
the --permissive flag, use the following command:
# docker run --security-opt label=disable -i -t fedora bash
If you want a tighter security policy on the processes within a con-
tainer, you can specify an alternate type for the container. You could
run a container that is only allowed to listen on Apache ports by exe-
cuting the following command:
# docker run --security-opt label=type:svirt_apache_t -i -t centos bash
Note:
You would have to write policy defining a svirt_apache_t type.
Setting device weight
If you want to set /dev/sda device weight to 200, you can specify the
device weight by --blkio-weight-device flag. Use the following command:
# docker run -it --blkio-weight-device "/dev/sda:200" ubuntu
Specify isolation technology for container (--isolation)
This option is useful in situations where you are running Docker con-
tainers on Microsoft Windows. The --isolation <value> option sets a
container's isolation technology. On Linux, the only supported is the
default option which uses Linux namespaces. These two commands are
equivalent on Linux:
$ docker run -d busybox top
$ docker run -d --isolation default busybox top
On Microsoft Windows, can take any of these values:
0
item default: Use the value specified by the Docker daemon's
--exec-opt . If the daemon does not specify an isolation tech-
nology, Microsoft Windows uses process as its default value.
item process: Namespace isolation only. item hyperv: Hyper-V
hypervisor partition-based isolation.
In practice, when running on Microsoft Windows without a daemon option
set, these two commands are equivalent:
$ docker run -d --isolation default busybox top
$ docker run -d --isolation process busybox top
If you have set the --exec-opt isolation=hyperv option on the Docker
daemon, any of these commands also result in hyperv isolation:
$ docker run -d --isolation default busybox top
$ docker run -d --isolation hyperv busybox top
HISTORY
April 2014, Originally compiled by William Henry (whenry at redhat dot
com) based on docker.com source material and internal work. June 2014,
updated by Sven Dowideit <[email protected]> July 2014, updated
by Sven Dowideit <[email protected]> November 2015, updated by
Sally O'Malley <[email protected]>
Docker Community Docker User Manuals DOCKER(1)
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