Docker runs processes in isolated containers. When an operator executes docker run, she 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 binary to run, the networking to expose, and more, but docker run gives final control to the operator who starts the container from the image. That's the main reason run has more options than any other docker command.
The basic docker run command takes this form:
$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
To learn how to interpret the types of [OPTIONS], see Option types.
The run options control the image's runtime behavior in a container. These settings affect:
An image developer may set defaults for these same settings when they create the image using the docker build command. Operators, however, can override all defaults set by the developer using the run options. And, operators can also override nearly all the defaults set by the Docker runtime itself.
Finally, depending on your Docker system configuration, you may be required to preface each docker command with sudo. To avoid having to use sudo with the docker command, your system administrator can create a Unix group called docker and add users to it. For more information about this configuration, refer to the Docker installation documentation for your operating system.
Only the operator (the person executing docker run) can set the following options.
When starting a Docker container, you must first decide if you want to run the container in the background in a “detached” mode or in the default foreground mode:
-d=false: Detached mode: Run container in the background, print new container id
In detached mode (-d=true or just -d), all I/O should be done through network connections or shared volumes because the container is no longer listening to the command line where you executed docker run. 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.
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 pretend to be a TTY (this is what most command line executables expect) and pass along signals. All of that is configurable:
-a=[] : Attach to `STDIN`, `STDOUT` and/or `STDERR` -t=false : Allocate a pseudo-tty --sig-proxy=true: Proxify all received signal to the process (non-TTY mode only) -i=false : Keep STDIN open even if not attached
If you do not specify -a then Docker will [attach all standard streams]( https://github.com/docker/docker/blob/ 75a7f4d90cde0295bcfb7213004abce8d4779b75/commands.go#L1797). You can specify to which of the three standard streams (STDIN, STDOUT, STDERR) you'd like to connect instead, as in:
$ docker run -a stdin -a stdout -i -t ubuntu /bin/bash
For interactive processes (like a shell), you must use -i -t together in order to allocate a tty for the container process. -i -t is often written -it as you'll see in later examples. Specifying -t is forbidden when the client standard output is redirected or piped, such as in: echo test | docker run -i busybox cat.
Note: A process running as PID 1 inside a container is treated specially by Linux: it ignores any signal with the default action. So, the process will not terminate on
SIGINTorSIGTERMunless it is coded to do so.
The operator can identify a container in three ways:
The UUID identifiers come from the Docker daemon, and if you do not assign a name to the container with --name then the daemon will also generate a random string name too. The name can become a handy way to add meaning to a container since you can use this name when defining links (or any other place you need to identify a container). This works for both background and foreground Docker containers.
Finally, to help with automation, you can have Docker write the container ID out to a file of your choosing. This is similar to how some programs might write out their process ID to a file (you've seen them as PID files):
--cidfile="": Write the container ID to the file
While not strictly a means of identifying a container, you can specify a version of an image you'd like to run the container with by adding image[:tag] to the command. For example, docker run ubuntu:14.04.
Images using the v2 or later image format have a content-addressable identifier called a digest. As long as the input used to generate the image is unchanged, the digest value is predictable and referenceable.
--pid="" : Set the PID (Process) Namespace mode for the container,
'host': use the host's PID namespace inside the container
By default, all containers have the PID namespace enabled.
PID namespace provides separation of processes. The PID Namespace removes the view of the system processes, and allows process ids to be reused including pid 1.
In certain cases you want your container to share the host's process namespace, basically allowing processes within the container to see all of the processes on the system. For example, you could build a container with debugging tools like strace or gdb, but want to use these tools when debugging processes within the container.
$ docker run --pid=host rhel7 strace -p 1234
This command would allow you to use strace inside the container on pid 1234 on the host.
--uts="" : Set the UTS namespace mode for the container,
'host': use the host's UTS namespace inside the container
The UTS namespace is for setting the hostname and the domain that is visible to running processes in that namespace. By default, all containers, including those with --net=host, have their own UTS namespace. The host setting will result in the container using the same UTS namespace as the host.
You may wish to share the UTS namespace with the host if you would like the hostname of the container to change as the hostname of the host changes. A more advanced use case would be changing the host's hostname from a container.
Note:
--uts="host"gives the container full access to change the hostname of the host and is therefore considered insecure.
--ipc="" : Set the IPC mode for the container,
'container:<name|id>': reuses another container's IPC namespace
'host': use the host's IPC namespace inside the container
By default, all containers have the IPC namespace enabled.
IPC (POSIX/SysV IPC) namespace provides separation of named shared memory segments, semaphores and message queues.
Shared memory segments are used to accelerate inter-process communication at memory speed, rather than through pipes or through the network stack. Shared memory is commonly used by databases and custom-built (typically C/OpenMPI, C++/using boost libraries) high performance applications for scientific computing and financial services industries. If these types of applications are broken into multiple containers, you might need to share the IPC mechanisms of the containers.
--dns=[] : Set custom dns servers for the container
--net="bridge" : Set the Network mode for the container
'bridge': creates a new network stack for the container on the docker bridge
'none': no networking for this container
'container:<name|id>': reuses another container network stack
'host': use the host network stack inside the container
--add-host="" : Add a line to /etc/hosts (host:IP)
--mac-address="" : Sets the container's Ethernet device's MAC address
By default, all containers have networking enabled and they can make any outgoing connections. The operator can completely disable networking with docker run --net none which disables all incoming and outgoing networking. In cases like this, you would perform I/O through files or STDIN and STDOUT only.
Publishing ports and linking to other containers will not work when --net is anything other than the default (bridge).
Your container will use the same DNS servers as the host by default, but you can override this with --dns.
By default, the MAC address is generated using the IP address allocated to the container. You can set the container's MAC address explicitly by providing a MAC address via the --mac-address parameter (format:12:34:56:78:9a:bc).
Supported networking modes are:
With the networking mode set to none a container will not have a access to any external routes. The container will still have a loopback interface enabled in the container but it does not have any routes to external traffic.
With the networking mode set to bridge a container will use docker‘s default networking setup. A bridge is setup on the host, commonly named docker0, and a pair of veth interfaces will be created for the container. One side of the veth pair will remain on the host attached to the bridge while the other side of the pair will be placed inside the container’s namespaces in addition to the loopback interface. An IP address will be allocated for containers on the bridge's network and traffic will be routed though this bridge to the container.
With the networking mode set to host a container will share the host‘s network stack and all interfaces from the host will be available to the container. The container’s hostname will match the hostname on the host system. Note that --add-host --hostname --dns --dns-search and --mac-address is invalid in host netmode.
Compared to the default bridge mode, the host mode gives significantly better networking performance since it uses the host's native networking stack whereas the bridge has to go through one level of virtualization through the docker daemon. It is recommended to run containers in this mode when their networking performance is critical, for example, a production Load Balancer or a High Performance Web Server.
Note:
--net="host"gives the container full access to local system services such as D-bus and is therefore considered insecure.
With the networking mode set to container a container will share the network stack of another container. The other container's name must be provided in the format of --net container:<name|id>. Note that --add-host --hostname --dns --dns-search and --mac-address is invalid in container netmode, and --publish --publish-all --expose are also invalid in container netmode.
Example running a Redis container with Redis binding to localhost then running the redis-cli command and connecting to the Redis server over the localhost interface.
$ docker run -d --name redis example/redis --bind 127.0.0.1 $ # use the redis container's network stack to access localhost $ docker run --rm -it --net container:redis example/redis-cli -h 127.0.0.1
Your container will have lines in /etc/hosts which define the hostname of the container itself as well as localhost and a few other common things. The --add-host flag can be used to add additional lines to /etc/hosts.
$ docker run -it --add-host db-static:86.75.30.9 ubuntu cat /etc/hosts 172.17.0.22 09d03f76bf2c fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters 127.0.0.1 localhost ::1 localhost ip6-localhost ip6-loopback 86.75.30.9 db-static
Using the --restart flag on Docker run you can specify a restart policy for how a container should or should not be restarted on exit.
When a restart policy is active on a container, it will be shown as either Up or Restarting in docker ps. It can also be useful to use docker events to see the restart policy in effect.
Docker supports the following restart policies:
An ever increasing delay (double the previous delay, starting at 100 milliseconds) is added before each restart to prevent flooding the server. This means the daemon will wait for 100 ms, then 200 ms, 400, 800, 1600, and so on until either the on-failure limit is hit, or when you docker stop or docker rm -f the container.
If a container is successfully restarted (the container is started and runs for at least 10 seconds), the delay is reset to its default value of 100 ms.
You can specify the maximum amount of times Docker will try to restart the container when using the on-failure policy. The default is that Docker will try forever to restart the container. The number of (attempted) restarts for a container can be obtained via docker inspect. For example, to get the number of restarts for container “my-container”;
$ docker inspect -f "{{ .RestartCount }}" my-container
# 2
Or, to get the last time the container was (re)started;
$ docker inspect -f "{{ .State.StartedAt }}" my-container
# 2015-03-04T23:47:07.691840179Z
You cannot set any restart policy in combination with “clean up (--rm)”. Setting both --restart and --rm results in an error.
$ docker run --restart=always redis
This will run the redis container with a restart policy of always so that if the container exits, Docker will restart it.
$ docker run --restart=on-failure:10 redis
This will run the redis container with a restart policy of on-failure and a maximum restart count of 10. If the redis container exits with a non-zero exit status more than 10 times in a row Docker will abort trying to restart the container. Providing a maximum restart limit is only valid for the on-failure policy.
By default a container‘s file system persists even after the container exits. This makes debugging a lot easier (since you can inspect the final state) and you retain all your data by default. But if you are running short-term foreground processes, these container file systems can really pile up. If instead you’d like Docker to automatically clean up the container and remove the file system when the container exits, you can add the --rm flag:
--rm=false: Automatically remove the container when it exits (incompatible with -d)
--security-opt="label:user:USER" : Set the label user for the container
--security-opt="label:role:ROLE" : Set the label role for the container
--security-opt="label:type:TYPE" : Set the label type for the container
--security-opt="label:level:LEVEL" : Set the label level for the container
--security-opt="label:disable" : Turn off label confinement for the container
--security-opt="apparmor:PROFILE" : Set the apparmor profile to be applied
to the container
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 containers.
$ 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 container, you can specify an alternate type for the container. You could run a container that is only allowed to listen on Apache ports by executing 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.
Using the --cgroup-parent flag, you can pass a specific cgroup to run a container in. This allows you to create and manage cgroups on their own. You can define custom resources for those cgroups and put containers under a common parent group.
The operator can also adjust the performance parameters of the container:
-m, --memory="": Memory limit (format: <number><optional unit>, where unit = b, k, m or g) --memory-swap="": Total memory limit (memory + swap, format: <number><optional unit>, where unit = b, k, m or g) -c, --cpu-shares=0: CPU shares (relative weight) --cpu-period=0: Limit the CPU CFS (Completely Fair Scheduler) period --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. --cpu-quota=0: Limit the CPU CFS (Completely Fair Scheduler) quota --blkio-weight=0: Block IO weight (relative weight) accepts a weight value between 10 and 1000. --oom-kill-disable=true|false: Whether to disable OOM Killer for the container or not. --memory-swappiness="": Tune a container's memory swappiness behavior. Accepts an integer between 0 and 100.
We have four ways to set memory usage:
Examples:
$ docker run -ti ubuntu:14.04 /bin/bash
We set nothing about memory, this means the processes in the container can use as much memory and swap memory as they need.
$ docker run -ti -m 300M --memory-swap -1 ubuntu:14.04 /bin/bash
We set memory limit and disabled swap memory limit, this means the processes in the container can use 300M memory and as much swap memory as they need (if the host supports swap memory).
$ docker run -ti -m 300M ubuntu:14.04 /bin/bash
We set memory limit only, this means the processes in the container can use 300M memory and 300M swap memory, by default, the total virtual memory size (--memory-swap) will be set as double of memory, in this case, memory + swap would be 2*300M, so processes can use 300M swap memory as well.
$ docker run -ti -m 300M --memory-swap 1G ubuntu:14.04 /bin/bash
We set both memory and swap memory, so the processes in the container can use 300M memory and 700M swap memory.
By default, kernel kills processes in a container if an out-of-memory (OOM) error occurs. To change this behaviour, use the --oom-kill-disable option. Only disable the OOM killer on containers where you have also set the -m/--memory option. If the -m flag is not set, this can result in the host running out of memory and require killing the host's system processes to free memory.
Examples:
The following example limits the memory to 100M and disables the OOM killer for this container:
$ docker run -ti -m 100M --oom-kill-disable ubuntu:14.04 /bin/bash
The following example, illustrates a dangerous way to use the flag:
$ docker run -ti --oom-kill-disable ubuntu:14.04 /bin/bash
The container has unlimited memory which can cause the host to run out memory and require killing system processes to free memory.
By default, a container's kernel can swap out a percentage of anonymous pages. To set this percentage for a container, specify a --memory-swappiness value between 0 and 100. A value of 0 turns off anonymous page swapping. A value of 100 sets all anonymous pages as swappable. By default, if you are not using --memory-swappiness, memory swappiness value will be inherited from the parent.
For example, you can set:
$ docker run -ti --memory-swappiness=0 ubuntu:14.04 /bin/bash
Setting the --memory-swappiness option is helpful when you want to retain the container's working set and to avoid swapping performance penalties.
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 -c or --cpu-shares flag to set the weighting to 2 or higher.
The proportion will only apply when CPU-intensive processes are running. When tasks in one container are idle, other containers can use the left-over CPU time. The actual amount of CPU time will vary depending 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 container {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
The default CPU CFS (Completely Fair Scheduler) period is 100ms. We can use --cpu-period to set the period of CPUs to limit the container's CPU usage. And usually --cpu-period should work with --cpu-quota.
Examples:
$ docker run -ti --cpu-period=50000 --cpu-quota=25000 ubuntu:14.04 /bin/bash
If there is 1 CPU, this means the container can get 50% CPU worth of run-time every 50ms.
For more information, see the CFS documentation on bandwidth limiting.
We can set cpus in which to allow execution for containers.
Examples:
$ docker run -ti --cpuset-cpus="1,3" ubuntu:14.04 /bin/bash
This means processes in container can be executed on cpu 1 and cpu 3.
$ docker run -ti --cpuset-cpus="0-2" ubuntu:14.04 /bin/bash
This means processes in container can be executed on cpu 0, cpu 1 and cpu 2.
We can set mems in which to allow execution for containers. Only effective on NUMA systems.
Examples:
$ docker run -ti --cpuset-mems="1,3" ubuntu:14.04 /bin/bash
This example restricts the processes in the container to only use memory from memory nodes 1 and 3.
$ docker run -ti --cpuset-mems="0-2" ubuntu:14.04 /bin/bash
This example restricts the processes in the container to only use memory from memory nodes 0, 1 and 2.
The --cpu-quota flag limits the container's CPU usage. The default 0 value allows the container to take 100% of a CPU resource (1 CPU). The CFS (Completely Fair Scheduler) handles resource allocation for executing processes and is default Linux Scheduler used by the kernel. Set this value to 50000 to limit the container to 50% of a CPU resource. For multiple CPUs, adjust the --cpu-quota as necessary. For more information, see the CFS documentation on bandwidth limiting.
By default, all containers get the same proportion of block IO bandwidth (blkio). This proportion is 500. To modify this proportion, change the container's blkio weight relative to the weighting of all other running containers using the --blkio-weight flag.
The --blkio-weight flag can set the weighting to a value between 10 to 1000. For example, the commands below create two containers with different blkio weight:
$ docker run -ti --name c1 --blkio-weight 300 ubuntu:14.04 /bin/bash $ docker run -ti --name c2 --blkio-weight 600 ubuntu:14.04 /bin/bash
If you do block IO in the two containers at the same time, by, for example:
$ time dd if=/mnt/zerofile of=test.out bs=1M count=1024 oflag=direct
You'll find that the proportion of time is the same as the proportion of blkio weights of the two containers.
Note: The blkio weight setting is only available for direct IO. Buffered IO is not currently supported.
--group-add: Add Linux capabilities
By default, the docker container process runs with the supplementary groups looked up for the specified user. If one wants to add more to that list of groups, then one can use this flag:
$ docker run -ti --rm --group-add audio --group-add dbus --group-add 777 busybox id uid=0(root) gid=0(root) groups=10(wheel),29(audio),81(dbus),777
--cap-add: Add Linux capabilities --cap-drop: Drop Linux capabilities --privileged=false: Give extended privileges to this container --device=[]: Allows you to run devices inside the container without the --privileged flag. --lxc-conf=[]: Add custom lxc options
By default, Docker containers are “unprivileged” and cannot, for example, run a Docker daemon inside a Docker container. This is because by default a container is not allowed to access any devices, but a “privileged” container is given access to all devices (see lxc-template.go and documentation on cgroups devices).
When the operator executes docker run --privileged, Docker will enable to access to all devices on the host as well as set some configuration in AppArmor or SELinux to allow the container nearly all the same access to the host as processes running outside containers on the host. Additional information about running with --privileged is available on the Docker Blog.
If you want to limit access to a specific device or devices you can use the --device flag. It allows you to specify one or more devices that will be accessible within the container.
$ docker run --device=/dev/snd:/dev/snd ...
By default, the container will be able to read, write, and mknod these devices. This can be overridden using a third :rwm set of options to each --device flag:
$ docker run --device=/dev/sda:/dev/xvdc --rm -it ubuntu fdisk /dev/xvdc
Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:r --rm -it ubuntu fdisk /dev/xvdc
You will not be able to write the partition table.
Command (m for help): q
$ docker run --device=/dev/sda:/dev/xvdc:w --rm -it ubuntu fdisk /dev/xvdc
crash....
$ docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk /dev/xvdc
fdisk: unable to open /dev/xvdc: Operation not permitted
In addition to --privileged, the operator can have fine grain control over the capabilities using --cap-add and --cap-drop. By default, Docker has a default list of capabilities that are kept. The following table lists the Linux capability options which can be added or dropped.
| Capability Key | Capability Description |
|---|---|
| SETPCAP | Modify process capabilities. |
| SYS_MODULE | Load and unload kernel modules. |
| SYS_RAWIO | Perform I/O port operations (iopl(2) and ioperm(2)). |
| SYS_PACCT | Use acct(2), switch process accounting on or off. |
| SYS_ADMIN | Perform a range of system administration operations. |
| SYS_NICE | Raise process nice value (nice(2), setpriority(2)) and change the nice value for arbitrary processes. |
| SYS_RESOURCE | Override resource Limits. |
| SYS_TIME | Set system clock (settimeofday(2), stime(2), adjtimex(2)); set real-time (hardware) clock. |
| SYS_TTY_CONFIG | Use vhangup(2); employ various privileged ioctl(2) operations on virtual terminals. |
| MKNOD | Create special files using mknod(2). |
| AUDIT_WRITE | Write records to kernel auditing log. |
| AUDIT_CONTROL | Enable and disable kernel auditing; change auditing filter rules; retrieve auditing status and filtering rules. |
| MAC_OVERRIDE | Allow MAC configuration or state changes. Implemented for the Smack LSM. |
| MAC_ADMIN | Override Mandatory Access Control (MAC). Implemented for the Smack Linux Security Module (LSM). |
| NET_ADMIN | Perform various network-related operations. |
| SYSLOG | Perform privileged syslog(2) operations. |
| CHOWN | Make arbitrary changes to file UIDs and GIDs (see chown(2)). |
| NET_RAW | Use RAW and PACKET sockets. |
| DAC_OVERRIDE | Bypass file read, write, and execute permission checks. |
| FOWNER | Bypass permission checks on operations that normally require the file system UID of the process to match the UID of the file. |
| DAC_READ_SEARCH | Bypass file read permission checks and directory read and execute permission checks. |
| FSETID | Don't clear set-user-ID and set-group-ID permission bits when a file is modified. |
| KILL | Bypass permission checks for sending signals. |
| SETGID | Make arbitrary manipulations of process GIDs and supplementary GID list. |
| SETUID | Make arbitrary manipulations of process UIDs. |
| LINUX_IMMUTABLE | Set the FS_APPEND_FL and FS_IMMUTABLE_FL i-node flags. |
| NET_BIND_SERVICE | Bind a socket to internet domain privileged ports (port numbers less than 1024). |
| NET_BROADCAST | Make socket broadcasts, and listen to multicasts. |
| IPC_LOCK | Lock memory (mlock(2), mlockall(2), mmap(2), shmctl(2)). |
| IPC_OWNER | Bypass permission checks for operations on System V IPC objects. |
| SYS_CHROOT | Use chroot(2), change root directory. |
| SYS_PTRACE | Trace arbitrary processes using ptrace(2). |
| SYS_BOOT | Use reboot(2) and kexec_load(2), reboot and load a new kernel for later execution. |
| LEASE | Establish leases on arbitrary files (see fcntl(2)). |
| SETFCAP | Set file capabilities. |
| WAKE_ALARM | Trigger something that will wake up the system. |
| BLOCK_SUSPEND | Employ features that can block system suspend. |
Further reference information is available on the capabilities(7) - Linux man page
Both flags support the value all, so if the operator wants to have all capabilities but MKNOD they could use:
$ docker run --cap-add=ALL --cap-drop=MKNOD ...
For interacting with the network stack, instead of using --privileged they should use --cap-add=NET_ADMIN to modify the network interfaces.
$ docker run -t -i --rm ubuntu:14.04 ip link add dummy0 type dummy RTNETLINK answers: Operation not permitted $ docker run -t -i --rm --cap-add=NET_ADMIN ubuntu:14.04 ip link add dummy0 type dummy
To mount a FUSE based filesystem, you need to combine both --cap-add and --device:
$ docker run --rm -it --cap-add SYS_ADMIN sshfs sshfs sven@10.10.10.20:/home/sven /mnt fuse: failed to open /dev/fuse: Operation not permitted $ docker run --rm -it --device /dev/fuse sshfs sshfs sven@10.10.10.20:/home/sven /mnt fusermount: mount failed: Operation not permitted $ docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse sshfs # sshfs sven@10.10.10.20:/home/sven /mnt The authenticity of host '10.10.10.20 (10.10.10.20)' can't be established. ECDSA key fingerprint is 25:34:85:75:25:b0:17:46:05:19:04:93:b5:dd:5f:c6. Are you sure you want to continue connecting (yes/no)? yes sven@10.10.10.20's password: root@30aa0cfaf1b5:/# ls -la /mnt/src/docker total 1516 drwxrwxr-x 1 1000 1000 4096 Dec 4 06:08 . drwxrwxr-x 1 1000 1000 4096 Dec 4 11:46 .. -rw-rw-r-- 1 1000 1000 16 Oct 8 00:09 .dockerignore -rwxrwxr-x 1 1000 1000 464 Oct 8 00:09 .drone.yml drwxrwxr-x 1 1000 1000 4096 Dec 4 06:11 .git -rw-rw-r-- 1 1000 1000 461 Dec 4 06:08 .gitignore ....
If the Docker daemon was started using the lxc exec-driver (docker -d --exec-driver=lxc) then the operator can also specify LXC options using one or more --lxc-conf parameters. These can be new parameters or override existing parameters from the lxc-template.go. Note that in the future, a given host's docker daemon may not use LXC, so this is an implementation-specific configuration meant for operators already familiar with using LXC directly.
Note: If you use
--lxc-confto modify a container‘s configuration which is also managed by the Docker daemon, then the Docker daemon will not know about this modification, and you will need to manage any conflicts yourself. For example, you can use--lxc-confto set a container’s IP address, but this will not be reflected in the/etc/hostsfile.
The container can have a different logging driver than the Docker daemon. Use the --log-driver=VALUE with the docker run command to configure the container's logging driver. The following options are supported:
none | Disables any logging for the container. docker logs won't be available with this driver. |
|---|---|
json-file | Default logging driver for Docker. Writes JSON messages to file. No logging options are supported for this driver. |
syslog | Syslog logging driver for Docker. Writes log messages to syslog. |
journald | Journald logging driver for Docker. Writes log messages to journald. |
gelf | Graylog Extended Log Format (GELF) logging driver for Docker. Writes log messages to a GELF endpoint likeGraylog or Logstash. |
fluentd | Fluentd logging driver for Docker. Writes log messages to fluentd (forward input). |
The `docker logs`command is available only for the `json-file` logging
driver. For detailed information on working with logging drivers, see Configure a logging driver.
Fluentd logging driver for Docker. Writes log messages to fluentd (forward input). docker logs command is not available for this logging driver.
Some options are supported by specifying --log-opt as many as needed, like --log-opt fluentd-address=localhost:24224 --log-opt fluentd-tag=docker.{{.Name}}.
fluentd-address: specify host:port to connect [localhost:24224]fluentd-tag: specify tag for fluentd message, which interpret some markup, ex {{.ID}}, {{.FullID}} or {{.Name}} [docker.{{.ID}}]When a developer builds an image from a Dockerfile or when she commits it, the developer can set a number of default parameters that take effect when the image starts up as a container.
Four of the Dockerfile commands cannot be overridden at runtime: FROM, MAINTAINER, RUN, and ADD. Everything else has a corresponding override in docker run. We'll go through what the developer might have set in each Dockerfile instruction and how the operator can override that setting.
Recall the optional COMMAND in the Docker commandline:
$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
This command is optional because the person who created the IMAGE may have already provided a default COMMAND using the Dockerfile CMD instruction. As the operator (the person running a container from the image), you can override that CMD instruction just by specifying a new COMMAND.
If the image also specifies an ENTRYPOINT then the CMD or COMMAND get appended as arguments to the ENTRYPOINT.
--entrypoint="": Overwrite the default entrypoint set by the image
The ENTRYPOINT of an image is similar to a COMMAND because it specifies what executable to run when the container 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 string to specify the new ENTRYPOINT. Here is an example of how to run a shell in a container that has been set up to automatically run something else (like /usr/bin/redis-server):
$ docker run -i -t --entrypoint /bin/bash example/redis
or two examples of how to pass more parameters to that ENTRYPOINT:
$ docker run -i -t --entrypoint /bin/bash example/redis -c ls -l $ docker run -i -t --entrypoint /usr/bin/redis-cli example/redis --help
The Dockerfile doesn‘t give much control over networking, only providing the EXPOSE instruction to give a hint to the operator about what incoming ports might provide services. The following options work with or override the Dockerfile’s exposed defaults:
--expose=[]: Expose a port or a range of ports from the container
without publishing it to your host
-P=false : Publish all exposed ports to the host interfaces
-p=[] : Publish a container᾿s port or a range of ports to the host
format: ip:hostPort:containerPort | ip::containerPort | hostPort:containerPort | containerPort
Both hostPort and containerPort can be specified 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., `-p 1234-1236:1234-1236/tcp`)
(use 'docker port' to see the actual mapping)
--link="" : Add link to another container (<name or id>:alias or <name or id>)
As mentioned previously, EXPOSE (and --expose) makes ports available in a container for incoming connections. The port number on the inside of the container (where the service listens) does not need to be the same number as the port exposed on the outside of the container (where clients connect), so inside the container you might have an HTTP service listening on port 80 (and so you EXPOSE 80 in the Dockerfile), but outside the container the port might be 42800.
To help a new client container reach the server container's internal port operator --expose'd by the operator or EXPOSE'd by the developer, the operator has three choices: start the server container with -P or -p, or start the client container with --link.
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 the 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.
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.
When a new container is created, Docker will set the following environment variables automatically:
The container may also include environment variables defined as a result of the container being linked with another container. See the Container Links section for more details.
Additionally, the operator can set any environment variable in the container by using one or more -e flags, even overriding those mentioned above, or already defined by the developer with a Dockerfile ENV:
$ docker run -e "deep=purple" --rm ubuntu /bin/bash -c export declare -x HOME="/" declare -x HOSTNAME="85bc26a0e200" declare -x OLDPWD declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" declare -x PWD="/" declare -x SHLVL="1" declare -x container="lxc" declare -x deep="purple"
Similarly the operator can set the hostname with -h.
--link <name or id>:alias also sets environment variables, using the alias string to define environment variables within the container that give the IP and PORT information for connecting to the service container. Let's imagine we have a container running Redis:
# Start the service container, named redis-name $ docker run -d --name redis-name dockerfiles/redis 4241164edf6f5aca5b0e9e4c9eccd899b0b8080c64c0cd26efe02166c73208f3 # The redis-name container exposed port 6379 $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 4241164edf6f $ dockerfiles/redis:latest /redis-stable/src/re 5 seconds ago Up 4 seconds 6379/tcp redis-name # Note that there are no public ports exposed since we didn᾿t use -p or -P $ docker port 4241164edf6f 6379 2014/01/25 00:55:38 Error: No public port '6379' published for 4241164edf6f
Yet we can get information about the Redis container's exposed ports with --link. Choose an alias that will form a valid environment variable!
$ docker run --rm --link redis-name:redis_alias --entrypoint /bin/bash dockerfiles/redis -c export declare -x HOME="/" declare -x HOSTNAME="acda7f7b1cdc" declare -x OLDPWD declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" declare -x PWD="/" declare -x REDIS_ALIAS_NAME="/distracted_wright/redis" declare -x REDIS_ALIAS_PORT="tcp://172.17.0.32:6379" declare -x REDIS_ALIAS_PORT_6379_TCP="tcp://172.17.0.32:6379" declare -x REDIS_ALIAS_PORT_6379_TCP_ADDR="172.17.0.32" declare -x REDIS_ALIAS_PORT_6379_TCP_PORT="6379" declare -x REDIS_ALIAS_PORT_6379_TCP_PROTO="tcp" declare -x SHLVL="1" declare -x container="lxc"
And we can use that information to connect from another container as a client:
$ docker run -i -t --rm --link redis-name:redis_alias --entrypoint /bin/bash dockerfiles/redis -c '/redis-stable/src/redis-cli -h $REDIS_ALIAS_PORT_6379_TCP_ADDR -p $REDIS_ALIAS_PORT_6379_TCP_PORT' 172.17.0.32:6379>
Docker will also map the private IP address to the alias of a linked container by inserting an entry into /etc/hosts. You can use this mechanism to communicate with a linked container by its alias:
$ docker run -d --name servicename busybox sleep 30 $ docker run -i -t --link servicename:servicealias busybox ping -c 1 servicealias
If you restart the source container (servicename in this case), the recipient container's /etc/hosts entry will be automatically updated.
Note: Unlike host entries in the
/etc/hostsfile, IP addresses stored in the environment variables are not automatically updated if the source container is restarted. We recommend using the host entries in/etc/hoststo resolve the IP address of linked containers.
-v=[]: Create a bind mount with: [host-dir:]container-dir[:rw|ro].
If 'host-dir' is missing, then docker creates a new volume.
If neither 'rw' or 'ro' is specified then the volume is mounted
in read-write mode.
--volumes-from="": Mount all volumes from the given container(s)
The volumes commands are complex enough to have their own documentation in section Managing data in containers. A developer can define one or more VOLUME's associated with an image, but only the operator can give access from one container to another (or from a container to a volume mounted on the host).
The default user within a container is root (id = 0), but if the developer created additional users, those are accessible too. The developer can set a default user to run the first process with the Dockerfile USER instruction, but the operator can override it:
-u="": Username or UID
Note: if you pass numeric uid, it must be in range 0-2147483647.
The default working directory for running binaries within a container is the root directory (/), but the developer can set a different default with the Dockerfile WORKDIR command. The operator can override this with:
-w="": Working directory inside the container