1---
2description: "Running and configuring containers with the Docker CLI"
3keywords: "docker, run, cli"
4aliases:
5- /reference/run/
6title: Running containers
7---
8
9Docker runs processes in isolated containers. A container is a process
10which runs on a host. The host may be local or remote. When an you
11execute `docker run`, the container process that runs is isolated in
12that it has its own file system, its own networking, and its own
13isolated process tree separate from the host.
14
15This page details how to use the `docker run` command to run containers.
16
17## General form
18
19A `docker run` command takes the following form:
20
21```console
22$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
23```
24
25The `docker run` command must specify an [image reference](#image-references)
26to create the container from.
27
28### Image references
29
30The image reference is the name and version of the image. You can use the image
31reference to create or run a container based on an image.
32
33- `docker run IMAGE[:TAG][@DIGEST]`
34- `docker create IMAGE[:TAG][@DIGEST]`
35
36An image tag is the image version, which defaults to `latest` when omitted. Use
37the tag to run a container from specific version of an image. For example, to
38run version `23.10` of the `ubuntu` image: `docker run ubuntu:23.10`.
39
40#### Image digests
41
42Images using the v2 or later image format have a content-addressable identifier
43called a digest. As long as the input used to generate the image is unchanged,
44the digest value is predictable.
45
46The following example runs a container from the `alpine` image with the
47`sha256:9cacb71397b640eca97488cf08582ae4e4068513101088e9f96c9814bfda95e0` digest:
48
49```console
50$ docker run alpine@sha256:9cacb71397b640eca97488cf08582ae4e4068513101088e9f96c9814bfda95e0 date
51```
52
53### Options
54
55`[OPTIONS]` let you configure options for the container. For example, you can
56give the container a name (`--name`), or run it as a background process (`-d`).
57You can also set options to control things like resource constraints and
58networking.
59
60### Commands and arguments
61
62You can use the `[COMMAND]` and `[ARG...]` positional arguments to specify
63commands and arguments for the container to run when it starts up. For example,
64you can specify `sh` as the `[COMMAND]`, combined with the `-i` and `-t` flags,
65to start an interactive shell in the container (if the image you select has an
66`sh` executable on `PATH`).
67
68```console
69$ docker run -it IMAGE sh
70```
71
72> **Note**
73>
74> Depending on your Docker system configuration, you may be
75> required to preface the `docker run` command with `sudo`. To avoid
76> having to use `sudo` with the `docker` command, your system
77> administrator can create a Unix group called `docker` and add users to
78> it. For more information about this configuration, refer to the Docker
79> installation documentation for your operating system.
80
81## Foreground and background
82
83When you start a container, the container runs in the foreground by default.
84If you want to run the container in the background instead, you can use the
85`--detach` (or `-d`) flag. This starts the container without occupying your
86terminal window.
87
88```console
89$ docker run -d <IMAGE>
90```
91
92While the container runs in the background, you can interact with the container
93using other CLI commands. For example, `docker logs` lets you view the logs for
94the container, and `docker attach` brings it to the foreground.
95
96```console
97$ docker run -d nginx
980246aa4d1448a401cabd2ce8f242192b6e7af721527e48a810463366c7ff54f1
99$ docker ps
100CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1010246aa4d1448 nginx "/docker-entrypoint.…" 2 seconds ago Up 1 second 80/tcp pedantic_liskov
102$ docker logs -n 5 0246aa4d1448
1032023/11/06 15:58:23 [notice] 1#1: start worker process 33
1042023/11/06 15:58:23 [notice] 1#1: start worker process 34
1052023/11/06 15:58:23 [notice] 1#1: start worker process 35
1062023/11/06 15:58:23 [notice] 1#1: start worker process 36
1072023/11/06 15:58:23 [notice] 1#1: start worker process 37
108$ docker attach 0246aa4d1448
109^C
1102023/11/06 15:58:40 [notice] 1#1: signal 2 (SIGINT) received, exiting
111...
112```
113
114For more information about `docker run` flags related to foreground and
115background modes, see:
116
117- [`docker run --detach`](https://docs.docker.com/reference/cli/docker/container/run/#detach): run container in background
118- [`docker run --attach`](https://docs.docker.com/reference/cli/docker/container/run/#attach): attach to `stdin`, `stdout`, and `stderr`
119- [`docker run --tty`](https://docs.docker.com/reference/cli/docker/container/run/#tty): allocate a pseudo-tty
120- [`docker run --interactive`](https://docs.docker.com/reference/cli/docker/container/run/#interactive): keep `stdin` open even if not attached
121
122For more information about re-attaching to a background container, see
123[`docker attach`](https://docs.docker.com/reference/cli/docker/container/attach/).
124
125## Container identification
126
127You can identify a container in three ways:
128
129| Identifier type | Example value |
130|:----------------------|:-------------------------------------------------------------------|
131| UUID long identifier | `f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778` |
132| UUID short identifier | `f78375b1c487` |
133| Name | `evil_ptolemy` |
134
135The UUID identifier is a random ID assigned to the container by the daemon.
136
137The daemon generates a random string name for containers automatically. You can
138also defined a custom name using [the `--name` flag](https://docs.docker.com/reference/cli/docker/container/run/#name).
139Defining a `name` can be a handy way to add meaning to a container. If you
140specify a `name`, you can use it when referring to the container in a
141user-defined network. This works for both background and foreground Docker
142containers.
143
144A container identifier is not the same thing as an image reference. The image
145reference specifies which image to use when you run a container. You can't run
146`docker exec nginx:alpine sh` to open a shell in a container based on the
147`nginx:alpine` image, because `docker exec` expects a container identifier
148(name or ID), not an image.
149
150While the image used by a container is not an identifier for the container, you
151find out the IDs of containers using an image by using the `--filter` flag. For
152example, the following `docker ps` command gets the IDs of all running
153containers based on the `nginx:alpine` image:
154
155```console
156$ docker ps -q --filter ancestor=nginx:alpine
157```
158
159For more information about using filters, see
160[Filtering](https://docs.docker.com/config/filter/).
161
162## Container networking
163
164Containers have networking enabled by default, and they can make outgoing
165connections. If you're running multiple containers that need to communicate
166with each other, you can create a custom network and attach the containers to
167the network.
168
169When multiple containers are attached to the same custom network, they can
170communicate with each other using the container names as a DNS hostname. The
171following example creates a custom network named `my-net`, and runs two
172containers that attach to the network.
173
174```console
175$ docker network create my-net
176$ docker run -d --name web --network my-net nginx:alpine
177$ docker run --rm -it --network my-net busybox
178/ # ping web
179PING web (172.18.0.2): 56 data bytes
18064 bytes from 172.18.0.2: seq=0 ttl=64 time=0.326 ms
18164 bytes from 172.18.0.2: seq=1 ttl=64 time=0.257 ms
18264 bytes from 172.18.0.2: seq=2 ttl=64 time=0.281 ms
183^C
184--- web ping statistics ---
1853 packets transmitted, 3 packets received, 0% packet loss
186round-trip min/avg/max = 0.257/0.288/0.326 ms
187```
188
189For more information about container networking, see [Networking
190overview](https://docs.docker.com/network/)
191
192## Filesystem mounts
193
194By default, the data in a container is stored in an ephemeral, writable
195container layer. Removing the container also removes its data. If you want to
196use persistent data with containers, you can use filesystem mounts to store the
197data persistently on the host system. Filesystem mounts can also let you share
198data between containers and the host.
199
200Docker supports two main categories of mounts:
201
202- Volume mounts
203- Bind mounts
204
205Volume mounts are great for persistently storing data for containers, and for
206sharing data between containers. Bind mounts, on the other hand, are for
207sharing data between a container and the host.
208
209You can add a filesystem mount to a container using the `--mount` flag for the
210`docker run` command.
211
212The following sections show basic examples of how to create volumes and bind
213mounts. For more in-depth examples and descriptions, refer to the section of
214the [storage section](https://docs.docker.com/storage/) in the documentation.
215
216### Volume mounts
217
218To create a volume mount:
219
220```console
221$ docker run --mount source=<VOLUME_NAME>,target=[PATH] [IMAGE] [COMMAND...]
222```
223
224The `--mount` flag takes two parameters in this case: `source` and `target`.
225The value for the `source` parameter is the name of the volume. The value of
226`target` is the mount location of the volume inside the container. Once you've
227created the volume, any data you write to the volume is persisted, even if you
228stop or remove the container:
229
230```console
231$ docker run --rm --mount source=my_volume,target=/foo busybox \
232 echo "hello, volume!" > /foo/hello.txt
233$ docker run --mount source=my_volume,target=/bar busybox
234 cat /bar/hello.txt
235hello, volume!
236```
237
238The `target` must always be an absolute path, such as `/src/docs`. An absolute
239path starts with a `/` (forward slash). Volume names must start with an
240alphanumeric character, followed by `a-z0-9`, `_` (underscore), `.` (period) or
241`-` (hyphen).
242
243### Bind mounts
244
245To create a bind mount:
246
247```console
248$ docker run -it --mount type=bind,source=[PATH],target=[PATH] busybox
249```
250
251In this case, the `--mount` flag takes three parameters. A type (`bind`), and
252two paths. The `source` path is a the location on the host that you want to
253bind mount into the container. The `target` path is the mount destination
254inside the container.
255
256Bind mounts are read-write by default, meaning that you can both read and write
257files to and from the mounted location from the container. Changes that you
258make, such as adding or editing files, are reflected on the host filesystem:
259
260```console
261$ docker run -it --mount type=bind,source=.,target=/foo busybox
262/ # echo "hello from container" > /foo/hello.txt
263/ # exit
264$ cat hello.txt
265hello from container
266```
267
268## Exit status
269
270The exit code from `docker run` gives information about why the container
271failed to run or why it exited. The following sections describe the meanings of
272different container exit codes values.
273
274### 125
275
276Exit code `125` indicates that the error is with Docker daemon itself.
277
278```console
279$ docker run --foo busybox; echo $?
280
281flag provided but not defined: --foo
282See 'docker run --help'.
283125
284```
285
286### 126
287
288Exit code `126` indicates that the specified contained command can't be invoked.
289The container command in the following example is: `/etc; echo $?`.
290
291```console
292$ docker run busybox /etc; echo $?
293
294docker: Error response from daemon: Container command '/etc' could not be invoked.
295126
296```
297
298### 127
299
300Exit code `127` indicates that the contained command can't be found.
301
302```console
303$ docker run busybox foo; echo $?
304
305docker: Error response from daemon: Container command 'foo' not found or does not exist.
306127
307```
308
309### Other exit codes
310
311Any exit code other than `125`, `126`, and `127` represent the exit code of the
312provided container command.
313
314```console
315$ docker run busybox /bin/sh -c 'exit 3'
316$ echo $?
3173
318```
319
320## Runtime constraints on resources
321
322The operator can also adjust the performance parameters of the
323container:
324
325| Option | Description |
326|:---------------------------|:-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
327| `-m`, `--memory=""` | Memory limit (format: `<number>[<unit>]`). Number is a positive integer. Unit can be one of `b`, `k`, `m`, or `g`. Minimum is 6M. |
328| `--memory-swap=""` | Total memory limit (memory + swap, format: `<number>[<unit>]`). Number is a positive integer. Unit can be one of `b`, `k`, `m`, or `g`. |
329| `--memory-reservation=""` | Memory soft limit (format: `<number>[<unit>]`). Number is a positive integer. Unit can be one of `b`, `k`, `m`, or `g`. |
330| `--kernel-memory=""` | Kernel memory limit (format: `<number>[<unit>]`). Number is a positive integer. Unit can be one of `b`, `k`, `m`, or `g`. Minimum is 4M. |
331| `-c`, `--cpu-shares=0` | CPU shares (relative weight) |
332| `--cpus=0.000` | Number of CPUs. Number is a fractional number. 0.000 means no limit. |
333| `--cpu-period=0` | Limit the CPU CFS (Completely Fair Scheduler) period |
334| `--cpuset-cpus=""` | CPUs in which to allow execution (0-3, 0,1) |
335| `--cpuset-mems=""` | Memory nodes (MEMs) in which to allow execution (0-3, 0,1). Only effective on NUMA systems. |
336| `--cpu-quota=0` | Limit the CPU CFS (Completely Fair Scheduler) quota |
337| `--cpu-rt-period=0` | Limit the CPU real-time period. In microseconds. Requires parent cgroups be set and cannot be higher than parent. Also check rtprio ulimits. |
338| `--cpu-rt-runtime=0` | Limit the CPU real-time runtime. In microseconds. Requires parent cgroups be set and cannot be higher than parent. Also check rtprio ulimits. |
339| `--blkio-weight=0` | Block IO weight (relative weight) accepts a weight value between 10 and 1000. |
340| `--blkio-weight-device=""` | Block IO weight (relative device weight, format: `DEVICE_NAME:WEIGHT`) |
341| `--device-read-bps=""` | Limit read rate from a device (format: `<device-path>:<number>[<unit>]`). Number is a positive integer. Unit can be one of `kb`, `mb`, or `gb`. |
342| `--device-write-bps=""` | Limit write rate to a device (format: `<device-path>:<number>[<unit>]`). Number is a positive integer. Unit can be one of `kb`, `mb`, or `gb`. |
343| `--device-read-iops="" ` | Limit read rate (IO per second) from a device (format: `<device-path>:<number>`). Number is a positive integer. |
344| `--device-write-iops="" ` | Limit write rate (IO per second) to a device (format: `<device-path>:<number>`). Number is a positive integer. |
345| `--oom-kill-disable=false` | Whether to disable OOM Killer for the container or not. |
346| `--oom-score-adj=0` | Tune container's OOM preferences (-1000 to 1000) |
347| `--memory-swappiness=""` | Tune a container's memory swappiness behavior. Accepts an integer between 0 and 100. |
348| `--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`. |
349
350### User memory constraints
351
352We have four ways to set user memory usage:
353
354<table>
355 <thead>
356 <tr>
357 <th>Option</th>
358 <th>Result</th>
359 </tr>
360 </thead>
361 <tbody>
362 <tr>
363 <td class="no-wrap">
364 <strong>memory=inf, memory-swap=inf</strong> (default)
365 </td>
366 <td>
367 There is no memory limit for the container. The container can use
368 as much memory as needed.
369 </td>
370 </tr>
371 <tr>
372 <td class="no-wrap"><strong>memory=L<inf, memory-swap=inf</strong></td>
373 <td>
374 (specify memory and set memory-swap as <code>-1</code>) The container is
375 not allowed to use more than L bytes of memory, but can use as much swap
376 as is needed (if the host supports swap memory).
377 </td>
378 </tr>
379 <tr>
380 <td class="no-wrap"><strong>memory=L<inf, memory-swap=2*L</strong></td>
381 <td>
382 (specify memory without memory-swap) The container is not allowed to
383 use more than L bytes of memory, swap <i>plus</i> memory usage is double
384 of that.
385 </td>
386 </tr>
387 <tr>
388 <td class="no-wrap">
389 <strong>memory=L<inf, memory-swap=S<inf, L<=S</strong>
390 </td>
391 <td>
392 (specify both memory and memory-swap) The container is not allowed to
393 use more than L bytes of memory, swap <i>plus</i> memory usage is limited
394 by S.
395 </td>
396 </tr>
397 </tbody>
398</table>
399
400Examples:
401
402```console
403$ docker run -it ubuntu:22.04 /bin/bash
404```
405
406We set nothing about memory, this means the processes in the container can use
407as much memory and swap memory as they need.
408
409```console
410$ docker run -it -m 300M --memory-swap -1 ubuntu:22.04 /bin/bash
411```
412
413We set memory limit and disabled swap memory limit, this means the processes in
414the container can use 300M memory and as much swap memory as they need (if the
415host supports swap memory).
416
417```console
418$ docker run -it -m 300M ubuntu:22.04 /bin/bash
419```
420
421We set memory limit only, this means the processes in the container can use
422300M memory and 300M swap memory, by default, the total virtual memory size
423(--memory-swap) will be set as double of memory, in this case, memory + swap
424would be 2*300M, so processes can use 300M swap memory as well.
425
426```console
427$ docker run -it -m 300M --memory-swap 1G ubuntu:22.04 /bin/bash
428```
429
430We set both memory and swap memory, so the processes in the container can use
431300M memory and 700M swap memory.
432
433Memory reservation is a kind of memory soft limit that allows for greater
434sharing of memory. Under normal circumstances, containers can use as much of
435the memory as needed and are constrained only by the hard limits set with the
436`-m`/`--memory` option. When memory reservation is set, Docker detects memory
437contention or low memory and forces containers to restrict their consumption to
438a reservation limit.
439
440Always set the memory reservation value below the hard limit, otherwise the hard
441limit takes precedence. A reservation of 0 is the same as setting no
442reservation. By default (without reservation set), memory reservation is the
443same as the hard memory limit.
444
445Memory reservation is a soft-limit feature and does not guarantee the limit
446won't be exceeded. Instead, the feature attempts to ensure that, when memory is
447heavily contended for, memory is allocated based on the reservation hints/setup.
448
449The following example limits the memory (`-m`) to 500M and sets the memory
450reservation to 200M.
451
452```console
453$ docker run -it -m 500M --memory-reservation 200M ubuntu:22.04 /bin/bash
454```
455
456Under this configuration, when the container consumes memory more than 200M and
457less than 500M, the next system memory reclaim attempts to shrink container
458memory below 200M.
459
460The following example set memory reservation to 1G without a hard memory limit.
461
462```console
463$ docker run -it --memory-reservation 1G ubuntu:22.04 /bin/bash
464```
465
466The container can use as much memory as it needs. The memory reservation setting
467ensures the container doesn't consume too much memory for long time, because
468every memory reclaim shrinks the container's consumption to the reservation.
469
470By default, kernel kills processes in a container if an out-of-memory (OOM)
471error occurs. To change this behaviour, use the `--oom-kill-disable` option.
472Only disable the OOM killer on containers where you have also set the
473`-m/--memory` option. If the `-m` flag is not set, this can result in the host
474running out of memory and require killing the host's system processes to free
475memory.
476
477The following example limits the memory to 100M and disables the OOM killer for
478this container:
479
480```console
481$ docker run -it -m 100M --oom-kill-disable ubuntu:22.04 /bin/bash
482```
483
484The following example, illustrates a dangerous way to use the flag:
485
486```console
487$ docker run -it --oom-kill-disable ubuntu:22.04 /bin/bash
488```
489
490The container has unlimited memory which can cause the host to run out memory
491and require killing system processes to free memory. The `--oom-score-adj`
492parameter can be changed to select the priority of which containers will
493be killed when the system is out of memory, with negative scores making them
494less likely to be killed, and positive scores more likely.
495
496### Kernel memory constraints
497
498Kernel memory is fundamentally different than user memory as kernel memory can't
499be swapped out. The inability to swap makes it possible for the container to
500block system services by consuming too much kernel memory. Kernel memory includes：
501
502 - stack pages
503 - slab pages
504 - sockets memory pressure
505 - tcp memory pressure
506
507You can setup kernel memory limit to constrain these kinds of memory. For example,
508every process consumes some stack pages. By limiting kernel memory, you can
509prevent new processes from being created when the kernel memory usage is too high.
510
511Kernel memory is never completely independent of user memory. Instead, you limit
512kernel memory in the context of the user memory limit. Assume "U" is the user memory
513limit and "K" the kernel limit. There are three possible ways to set limits:
514
515<table>
516 <thead>
517 <tr>
518 <th>Option</th>
519 <th>Result</th>
520 </tr>
521 </thead>
522 <tbody>
523 <tr>
524 <td class="no-wrap"><strong>U != 0, K = inf</strong> (default)</td>
525 <td>
526 This is the standard memory limitation mechanism already present before using
527 kernel memory. Kernel memory is completely ignored.
528 </td>
529 </tr>
530 <tr>
531 <td class="no-wrap"><strong>U != 0, K < U</strong></td>
532 <td>
533 Kernel memory is a subset of the user memory. This setup is useful in
534 deployments where the total amount of memory per-cgroup is overcommitted.
535 Overcommitting kernel memory limits is definitely not recommended, since the
536 box can still run out of non-reclaimable memory.
537 In this case, you can configure K so that the sum of all groups is
538 never greater than the total memory. Then, freely set U at the expense of
539 the system's service quality.
540 </td>
541 </tr>
542 <tr>
543 <td class="no-wrap"><strong>U != 0, K > U</strong></td>
544 <td>
545 Since kernel memory charges are also fed to the user counter and reclamation
546 is triggered for the container for both kinds of memory. This configuration
547 gives the admin a unified view of memory. It is also useful for people
548 who just want to track kernel memory usage.
549 </td>
550 </tr>
551 </tbody>
552</table>
553
554Examples:
555
556```console
557$ docker run -it -m 500M --kernel-memory 50M ubuntu:22.04 /bin/bash
558```
559
560We set memory and kernel memory, so the processes in the container can use
561500M memory in total, in this 500M memory, it can be 50M kernel memory tops.
562
563```console
564$ docker run -it --kernel-memory 50M ubuntu:22.04 /bin/bash
565```
566
567We set kernel memory without **-m**, so the processes in the container can
568use as much memory as they want, but they can only use 50M kernel memory.
569
570### Swappiness constraint
571
572By default, a container's kernel can swap out a percentage of anonymous pages.
573To set this percentage for a container, specify a `--memory-swappiness` value
574between 0 and 100. A value of 0 turns off anonymous page swapping. A value of
575100 sets all anonymous pages as swappable. By default, if you are not using
576`--memory-swappiness`, memory swappiness value will be inherited from the parent.
577
578For example, you can set:
579
580```console
581$ docker run -it --memory-swappiness=0 ubuntu:22.04 /bin/bash
582```
583
584Setting the `--memory-swappiness` option is helpful when you want to retain the
585container's working set and to avoid swapping performance penalties.
586
587### CPU share constraint
588
589By default, all containers get the same proportion of CPU cycles. This proportion
590can be modified by changing the container's CPU share weighting relative
591to the weighting of all other running containers.
592
593To modify the proportion from the default of 1024, use the `-c` or `--cpu-shares`
594flag to set the weighting to 2 or higher. If 0 is set, the system will ignore the
595value and use the default of 1024.
596
597The proportion will only apply when CPU-intensive processes are running.
598When tasks in one container are idle, other containers can use the
599left-over CPU time. The actual amount of CPU time will vary depending on
600the number of containers running on the system.
601
602For example, consider three containers, one has a cpu-share of 1024 and
603two others have a cpu-share setting of 512. When processes in all three
604containers attempt to use 100% of CPU, the first container would receive
60550% of the total CPU time. If you add a fourth container with a cpu-share
606of 1024, the first container only gets 33% of the CPU. The remaining containers
607receive 16.5%, 16.5% and 33% of the CPU.
608
609On a multi-core system, the shares of CPU time are distributed over all CPU
610cores. Even if a container is limited to less than 100% of CPU time, it can
611use 100% of each individual CPU core.
612
613For example, consider a system with more than three cores. If you start one
614container `{C0}` with `-c=512` running one process, and another container
615`{C1}` with `-c=1024` running two processes, this can result in the following
616division of CPU shares:
617
618 PID container CPU CPU share
619 100 {C0} 0 100% of CPU0
620 101 {C1} 1 100% of CPU1
621 102 {C1} 2 100% of CPU2
622
623### CPU period constraint
624
625The default CPU CFS (Completely Fair Scheduler) period is 100ms. We can use
626`--cpu-period` to set the period of CPUs to limit the container's CPU usage.
627And usually `--cpu-period` should work with `--cpu-quota`.
628
629Examples:
630
631```console
632$ docker run -it --cpu-period=50000 --cpu-quota=25000 ubuntu:22.04 /bin/bash
633```
634
635If there is 1 CPU, this means the container can get 50% CPU worth of run-time every 50ms.
636
637In addition to use `--cpu-period` and `--cpu-quota` for setting CPU period constraints,
638it is possible to specify `--cpus` with a float number to achieve the same purpose.
639For example, if there is 1 CPU, then `--cpus=0.5` will achieve the same result as
640setting `--cpu-period=50000` and `--cpu-quota=25000` (50% CPU).
641
642The default value for `--cpus` is `0.000`, which means there is no limit.
643
644For more information, see the [CFS documentation on bandwidth limiting](https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt).
645
646### Cpuset constraint
647
648We can set cpus in which to allow execution for containers.
649
650Examples:
651
652```console
653$ docker run -it --cpuset-cpus="1,3" ubuntu:22.04 /bin/bash
654```
655
656This means processes in container can be executed on cpu 1 and cpu 3.
657
658```console
659$ docker run -it --cpuset-cpus="0-2" ubuntu:22.04 /bin/bash
660```
661
662This means processes in container can be executed on cpu 0, cpu 1 and cpu 2.
663
664We can set mems in which to allow execution for containers. Only effective
665on NUMA systems.
666
667Examples:
668
669```console
670$ docker run -it --cpuset-mems="1,3" ubuntu:22.04 /bin/bash
671```
672
673This example restricts the processes in the container to only use memory from
674memory nodes 1 and 3.
675
676```console
677$ docker run -it --cpuset-mems="0-2" ubuntu:22.04 /bin/bash
678```
679
680This example restricts the processes in the container to only use memory from
681memory nodes 0, 1 and 2.
682
683### CPU quota constraint
684
685The `--cpu-quota` flag limits the container's CPU usage. The default 0 value
686allows the container to take 100% of a CPU resource (1 CPU). The CFS (Completely Fair
687Scheduler) handles resource allocation for executing processes and is default
688Linux Scheduler used by the kernel. Set this value to 50000 to limit the container
689to 50% of a CPU resource. For multiple CPUs, adjust the `--cpu-quota` as necessary.
690For more information, see the [CFS documentation on bandwidth limiting](https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt).
691
692### Block IO bandwidth (Blkio) constraint
693
694By default, all containers get the same proportion of block IO bandwidth
695(blkio). This proportion is 500. To modify this proportion, change the
696container's blkio weight relative to the weighting of all other running
697containers using the `--blkio-weight` flag.
698
699> **Note:**
700>
701> The blkio weight setting is only available for direct IO. Buffered IO is not
702> currently supported.
703
704The `--blkio-weight` flag can set the weighting to a value between 10 to 1000.
705For example, the commands below create two containers with different blkio
706weight:
707
708```console
709$ docker run -it --name c1 --blkio-weight 300 ubuntu:22.04 /bin/bash
710$ docker run -it --name c2 --blkio-weight 600 ubuntu:22.04 /bin/bash
711```
712
713If you do block IO in the two containers at the same time, by, for example:
714
715```console
716$ time dd if=/mnt/zerofile of=test.out bs=1M count=1024 oflag=direct
717```
718
719You'll find that the proportion of time is the same as the proportion of blkio
720weights of the two containers.
721
722The `--blkio-weight-device="DEVICE_NAME:WEIGHT"` flag sets a specific device weight.
723The `DEVICE_NAME:WEIGHT` is a string containing a colon-separated device name and weight.
724For example, to set `/dev/sda` device weight to `200`:
725
726```console
727$ docker run -it \
728 --blkio-weight-device "/dev/sda:200" \
729 ubuntu
730```
731
732If you specify both the `--blkio-weight` and `--blkio-weight-device`, Docker
733uses the `--blkio-weight` as the default weight and uses `--blkio-weight-device`
734to override this default with a new value on a specific device.
735The following example uses a default weight of `300` and overrides this default
736on `/dev/sda` setting that weight to `200`:
737
738```console
739$ docker run -it \
740 --blkio-weight 300 \
741 --blkio-weight-device "/dev/sda:200" \
742 ubuntu
743```
744
745The `--device-read-bps` flag limits the read rate (bytes per second) from a device.
746For example, this command creates a container and limits the read rate to `1mb`
747per second from `/dev/sda`:
748
749```console
750$ docker run -it --device-read-bps /dev/sda:1mb ubuntu
751```
752
753The `--device-write-bps` flag limits the write rate (bytes per second) to a device.
754For example, this command creates a container and limits the write rate to `1mb`
755per second for `/dev/sda`:
756
757```console
758$ docker run -it --device-write-bps /dev/sda:1mb ubuntu
759```
760
761Both flags take limits in the `<device-path>:<limit>[unit]` format. Both read
762and write rates must be a positive integer. You can specify the rate in `kb`
763(kilobytes), `mb` (megabytes), or `gb` (gigabytes).
764
765The `--device-read-iops` flag limits read rate (IO per second) from a device.
766For example, this command creates a container and limits the read rate to
767`1000` IO per second from `/dev/sda`:
768
769```console
770$ docker run -ti --device-read-iops /dev/sda:1000 ubuntu
771```
772
773The `--device-write-iops` flag limits write rate (IO per second) to a device.
774For example, this command creates a container and limits the write rate to
775`1000` IO per second to `/dev/sda`:
776
777```console
778$ docker run -ti --device-write-iops /dev/sda:1000 ubuntu
779```
780
781Both flags take limits in the `<device-path>:<limit>` format. Both read and
782write rates must be a positive integer.
783
784## Additional groups
785
786```console
787--group-add: Add additional groups to run as
788```
789
790By default, the docker container process runs with the supplementary groups looked
791up for the specified user. If one wants to add more to that list of groups, then
792one can use this flag:
793
794```console
795$ docker run --rm --group-add audio --group-add nogroup --group-add 777 busybox id
796
797uid=0(root) gid=0(root) groups=10(wheel),29(audio),99(nogroup),777
798```
799
800## Runtime privilege and Linux capabilities
801
802| Option | Description |
803|:---------------|:------------------------------------------------------------------------------|
804| `--cap-add` | Add Linux capabilities |
805| `--cap-drop` | Drop Linux capabilities |
806| `--privileged` | Give extended privileges to this container |
807| `--device=[]` | Allows you to run devices inside the container without the `--privileged` flag. |
808
809By default, Docker containers are "unprivileged" and cannot, for
810example, run a Docker daemon inside a Docker container. This is because
811by default a container is not allowed to access any devices, but a
812"privileged" container is given access to all devices (see
813the documentation on [cgroups devices](https://www.kernel.org/doc/Documentation/cgroup-v1/devices.txt)).
814
815The `--privileged` flag gives all capabilities to the container. When the operator
816executes `docker run --privileged`, Docker will enable access to all devices on
817the host as well as set some configuration in AppArmor or SELinux to allow the
818container nearly all the same access to the host as processes running outside
819containers on the host. Additional information about running with `--privileged`
820is available on the [Docker Blog](https://www.docker.com/blog/docker-can-now-run-within-docker/).
821
822If you want to limit access to a specific device or devices you can use
823the `--device` flag. It allows you to specify one or more devices that
824will be accessible within the container.
825
826```console
827$ docker run --device=/dev/snd:/dev/snd ...
828```
829
830By default, the container will be able to `read`, `write`, and `mknod` these devices.
831This can be overridden using a third `:rwm` set of options to each `--device` flag:
832
833```console
834$ docker run --device=/dev/sda:/dev/xvdc --rm -it ubuntu fdisk /dev/xvdc
835
836Command (m for help): q
837$ docker run --device=/dev/sda:/dev/xvdc:r --rm -it ubuntu fdisk /dev/xvdc
838You will not be able to write the partition table.
839
840Command (m for help): q
841
842$ docker run --device=/dev/sda:/dev/xvdc:w --rm -it ubuntu fdisk /dev/xvdc
843 crash....
844
845$ docker run --device=/dev/sda:/dev/xvdc:m --rm -it ubuntu fdisk /dev/xvdc
846fdisk: unable to open /dev/xvdc: Operation not permitted
847```
848
849In addition to `--privileged`, the operator can have fine grain control over the
850capabilities using `--cap-add` and `--cap-drop`. By default, Docker has a default
851list of capabilities that are kept. The following table lists the Linux capability
852options which are allowed by default and can be dropped.
853
854| Capability Key | Capability Description |
855|:----------------------|:-------------------------------------------------------------------------------------------------------------------------------|
856| AUDIT_WRITE | Write records to kernel auditing log. |
857| CHOWN | Make arbitrary changes to file UIDs and GIDs (see chown(2)). |
858| DAC_OVERRIDE | Bypass file read, write, and execute permission checks. |
859| FOWNER | Bypass permission checks on operations that normally require the file system UID of the process to match the UID of the file. |
860| FSETID | Don't clear set-user-ID and set-group-ID permission bits when a file is modified. |
861| KILL | Bypass permission checks for sending signals. |
862| MKNOD | Create special files using mknod(2). |
863| NET_BIND_SERVICE | Bind a socket to internet domain privileged ports (port numbers less than 1024). |
864| NET_RAW | Use RAW and PACKET sockets. |
865| SETFCAP | Set file capabilities. |
866| SETGID | Make arbitrary manipulations of process GIDs and supplementary GID list. |
867| SETPCAP | Modify process capabilities. |
868| SETUID | Make arbitrary manipulations of process UIDs. |
869| SYS_CHROOT | Use chroot(2), change root directory. |
870
871The next table shows the capabilities which are not granted by default and may be added.
872
873| Capability Key | Capability Description |
874|:----------------------|:-------------------------------------------------------------------------------------------------------------------------------|
875| AUDIT_CONTROL | Enable and disable kernel auditing; change auditing filter rules; retrieve auditing status and filtering rules. |
876| AUDIT_READ | Allow reading the audit log via multicast netlink socket. |
877| BLOCK_SUSPEND | Allow preventing system suspends. |
878| BPF | Allow creating BPF maps, loading BPF Type Format (BTF) data, retrieve JITed code of BPF programs, and more. |
879| CHECKPOINT_RESTORE | Allow checkpoint/restore related operations. Introduced in kernel 5.9. |
880| DAC_READ_SEARCH | Bypass file read permission checks and directory read and execute permission checks. |
881| IPC_LOCK | Lock memory (mlock(2), mlockall(2), mmap(2), shmctl(2)). |
882| IPC_OWNER | Bypass permission checks for operations on System V IPC objects. |
883| LEASE | Establish leases on arbitrary files (see fcntl(2)). |
884| LINUX_IMMUTABLE | Set the FS_APPEND_FL and FS_IMMUTABLE_FL i-node flags. |
885| MAC_ADMIN | Allow MAC configuration or state changes. Implemented for the Smack LSM. |
886| MAC_OVERRIDE | Override Mandatory Access Control (MAC). Implemented for the Smack Linux Security Module (LSM). |
887| NET_ADMIN | Perform various network-related operations. |
888| NET_BROADCAST | Make socket broadcasts, and listen to multicasts. |
889| PERFMON | Allow system performance and observability privileged operations using perf_events, i915_perf and other kernel subsystems |
890| SYS_ADMIN | Perform a range of system administration operations. |
891| SYS_BOOT | Use reboot(2) and kexec_load(2), reboot and load a new kernel for later execution. |
892| SYS_MODULE | Load and unload kernel modules. |
893| SYS_NICE | Raise process nice value (nice(2), setpriority(2)) and change the nice value for arbitrary processes. |
894| SYS_PACCT | Use acct(2), switch process accounting on or off. |
895| SYS_PTRACE | Trace arbitrary processes using ptrace(2). |
896| SYS_RAWIO | Perform I/O port operations (iopl(2) and ioperm(2)). |
897| SYS_RESOURCE | Override resource Limits. |
898| SYS_TIME | Set system clock (settimeofday(2), stime(2), adjtimex(2)); set real-time (hardware) clock. |
899| SYS_TTY_CONFIG | Use vhangup(2); employ various privileged ioctl(2) operations on virtual terminals. |
900| SYSLOG | Perform privileged syslog(2) operations. |
901| WAKE_ALARM | Trigger something that will wake up the system. |
902
903Further reference information is available on the [capabilities(7) - Linux man page](https://man7.org/linux/man-pages/man7/capabilities.7.html),
904and in the [Linux kernel source code](https://github.com/torvalds/linux/blob/124ea650d3072b005457faed69909221c2905a1f/include/uapi/linux/capability.h).
905
906Both flags support the value `ALL`, so to allow a container to use all capabilities
907except for `MKNOD`:
908
909```console
910$ docker run --cap-add=ALL --cap-drop=MKNOD ...
911```
912
913The `--cap-add` and `--cap-drop` flags accept capabilities to be specified with
914a `CAP_` prefix. The following examples are therefore equivalent:
915
916```console
917$ docker run --cap-add=SYS_ADMIN ...
918$ docker run --cap-add=CAP_SYS_ADMIN ...
919```
920
921For interacting with the network stack, instead of using `--privileged` they
922should use `--cap-add=NET_ADMIN` to modify the network interfaces.
923
924```console
925$ docker run -it --rm ubuntu:22.04 ip link add dummy0 type dummy
926
927RTNETLINK answers: Operation not permitted
928
929$ docker run -it --rm --cap-add=NET_ADMIN ubuntu:22.04 ip link add dummy0 type dummy
930```
931
932To mount a FUSE based filesystem, you need to combine both `--cap-add` and
933`--device`:
934
935```console
936$ docker run --rm -it --cap-add SYS_ADMIN sshfs sshfs sven@10.10.10.20:/home/sven /mnt
937
938fuse: failed to open /dev/fuse: Operation not permitted
939
940$ docker run --rm -it --device /dev/fuse sshfs sshfs sven@10.10.10.20:/home/sven /mnt
941
942fusermount: mount failed: Operation not permitted
943
944$ docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse sshfs
945
946# sshfs sven@10.10.10.20:/home/sven /mnt
947The authenticity of host '10.10.10.20 (10.10.10.20)' can't be established.
948ECDSA key fingerprint is 25:34:85:75:25:b0:17:46:05:19:04:93:b5:dd:5f:c6.
949Are you sure you want to continue connecting (yes/no)? yes
950sven@10.10.10.20's password:
951
952root@30aa0cfaf1b5:/# ls -la /mnt/src/docker
953
954total 1516
955drwxrwxr-x 1 1000 1000 4096 Dec 4 06:08 .
956drwxrwxr-x 1 1000 1000 4096 Dec 4 11:46 ..
957-rw-rw-r-- 1 1000 1000 16 Oct 8 00:09 .dockerignore
958-rwxrwxr-x 1 1000 1000 464 Oct 8 00:09 .drone.yml
959drwxrwxr-x 1 1000 1000 4096 Dec 4 06:11 .git
960-rw-rw-r-- 1 1000 1000 461 Dec 4 06:08 .gitignore
961....
962```
963
964The default seccomp profile will adjust to the selected capabilities, in order to allow
965use of facilities allowed by the capabilities, so you should not have to adjust this.
966
967## Overriding image defaults
968
969When you build an image from a [Dockerfile](https://docs.docker.com/reference/dockerfile/),
970or when committing it, you can set a number of default parameters that take
971effect when the image starts up as a container. When you run an image, you can
972override those defaults using flags for the `docker run` command.
973
974- [Default entrypoint](#default-entrypoint)
975- [Default command and options](#default-command-and-options)
976- [Expose ports](#exposed-ports)
977- [Environment variables](#environment-variables)
978- [Healthcheck](#healthchecks)
979- [User](#user)
980- [Working directory](#working-directory)
981
982### Default command and options
983
984The command syntax for `docker run` supports optionally specifying commands and
985arguments to the container's entrypoint, represented as `[COMMAND]` and
986`[ARG...]` in the following synopsis example:
987
988```console
989$ docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]
990```
991
992This command is optional because whoever created the `IMAGE` may have already
993provided a default `COMMAND`, using the Dockerfile `CMD` instruction. When you
994run a container, you can override that `CMD` instruction just by specifying a
995new `COMMAND`.
996
997If the image also specifies an `ENTRYPOINT` then the `CMD` or `COMMAND`
998get appended as arguments to the `ENTRYPOINT`.
999
1000### Default entrypoint
1001
1002```text
1003--entrypoint="": Overwrite the default entrypoint set by the image
1004```
1005
1006The entrypoint refers to the default executable that's invoked when you run a
1007container. A container's entrypoint is defined using the Dockerfile
1008`ENTRYPOINT` instruction. It's similar to specifying a default command because
1009it specifies, but the difference is that you need to pass an explicit flag to
1010override the entrypoint, whereas you can override default commands with
1011positional arguments. The defines a container's default behavior, with the idea
1012that when you set an entrypoint you can run the container *as if it were that
1013binary*, complete with default options, and you can pass in more options as
1014commands. But there are cases where you may want to run something else inside
1015the container. This is when overriding the default entrypoint at runtime comes
1016in handy, using the `--entrypoint` flag for the `docker run` command.
1017
1018The `--entrypoint` flag expects a string value, representing the name or path
1019of the binary that you want to invoke when the container starts. The following
1020example shows you how to run a Bash shell in a container that has been set up
1021to automatically run some other binary (like `/usr/bin/redis-server`):
1022
1023```console
1024$ docker run -it --entrypoint /bin/bash example/redis
1025```
1026
1027The following examples show how to pass additional parameters to the custom
1028entrypoint, using the positional command arguments:
1029
1030```console
1031$ docker run -it --entrypoint /bin/bash example/redis -c ls -l
1032$ docker run -it --entrypoint /usr/bin/redis-cli example/redis --help
1033```
1034
1035You can reset a containers entrypoint by passing an empty string, for example:
1036
1037```console
1038$ docker run -it --entrypoint="" mysql bash
1039```
1040
1041> **Note**
1042>
1043> Passing `--entrypoint` clears out any default command set on the image. That
1044> is, any `CMD` instruction in the Dockerfile used to build it.
1045
1046### Exposed ports
1047
1048By default, when you run a container, none of the container's ports are exposed
1049to the host. This means you won't be able to access any ports that the
1050container might be listening on. To make a container's ports accessible from
1051the host, you need to publish the ports.
1052
1053You can start the container with the `-P` or `-p` flags to expose its ports:
1054
1055- The `-P` (or `--publish-all`) flag publishes all the exposed ports to the
1056 host. Docker binds each exposed port to a random port on the host.
1057
1058 The `-P` flag only publishes port numbers that are explicitly flagged as
1059 exposed, either using the Dockerfile `EXPOSE` instruction or the `--expose`
1060 flag for the `docker run` command.
1061
1062- The `-p` (or `--publish`) flag lets you explicitly map a single port or range
1063 of ports in the container to the host.
1064
1065The port number inside the container (where the service listens) doesn't need
1066to match the port number published on the outside of the container (where
1067clients connect). For example, inside the container an HTTP service might be
1068listening on port 80. At runtime, the port might be bound to 42800 on the host.
1069To find the mapping between the host ports and the exposed ports, use the
1070`docker port` command.
1071
1072### Environment variables
1073
1074Docker automatically sets some environment variables when creating a Linux
1075container. Docker doesn't set any environment variables when creating a Windows
1076container.
1077
1078The following environment variables are set for Linux containers:
1079
1080| Variable | Value |
1081|:-----------|:-----------------------------------------------------------------------------------------------------|
1082| `HOME` | Set based on the value of `USER` |
1083| `HOSTNAME` | The hostname associated with the container |
1084| `PATH` | Includes popular directories, such as `/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin` |
1085| `TERM` | `xterm` if the container is allocated a pseudo-TTY |
1086
1087
1088Additionally, you can set any environment variable in the container by using
1089one or more `-e` flags. You can even override the variables mentioned above, or
1090variables defined using a Dockerfile `ENV` instruction when building the image.
1091
1092If the you name an environment variable without specifying a value, the current
1093value of the named variable on the host is propagated into the container's
1094environment:
1095
1096```console
1097$ export today=Wednesday
1098$ docker run -e "deep=purple" -e today --rm alpine env
1099
1100PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
1101HOSTNAME=d2219b854598
1102deep=purple
1103today=Wednesday
1104HOME=/root
1105```
1106
1107```powershell
1108PS C:\> docker run --rm -e "foo=bar" microsoft/nanoserver cmd /s /c set
1109ALLUSERSPROFILE=C:\ProgramData
1110APPDATA=C:\Users\ContainerAdministrator\AppData\Roaming
1111CommonProgramFiles=C:\Program Files\Common Files
1112CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files
1113CommonProgramW6432=C:\Program Files\Common Files
1114COMPUTERNAME=C2FAEFCC8253
1115ComSpec=C:\Windows\system32\cmd.exe
1116foo=bar
1117LOCALAPPDATA=C:\Users\ContainerAdministrator\AppData\Local
1118NUMBER_OF_PROCESSORS=8
1119OS=Windows_NT
1120Path=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Users\ContainerAdministrator\AppData\Local\Microsoft\WindowsApps
1121PATHEXT=.COM;.EXE;.BAT;.CMD
1122PROCESSOR_ARCHITECTURE=AMD64
1123PROCESSOR_IDENTIFIER=Intel64 Family 6 Model 62 Stepping 4, GenuineIntel
1124PROCESSOR_LEVEL=6
1125PROCESSOR_REVISION=3e04
1126ProgramData=C:\ProgramData
1127ProgramFiles=C:\Program Files
1128ProgramFiles(x86)=C:\Program Files (x86)
1129ProgramW6432=C:\Program Files
1130PROMPT=$P$G
1131PUBLIC=C:\Users\Public
1132SystemDrive=C:
1133SystemRoot=C:\Windows
1134TEMP=C:\Users\ContainerAdministrator\AppData\Local\Temp
1135TMP=C:\Users\ContainerAdministrator\AppData\Local\Temp
1136USERDOMAIN=User Manager
1137USERNAME=ContainerAdministrator
1138USERPROFILE=C:\Users\ContainerAdministrator
1139windir=C:\Windows
1140```
1141
1142### Healthchecks
1143
1144The following flags for the `docker run` command let you control the parameters
1145for container healthchecks:
1146
1147| Option | Description |
1148|:---------------------------|:---------------------------------------------------------------------------------------|
1149| `--health-cmd` | Command to run to check health |
1150| `--health-interval` | Time between running the check |
1151| `--health-retries` | Consecutive failures needed to report unhealthy |
1152| `--health-timeout` | Maximum time to allow one check to run |
1153| `--health-start-period` | Start period for the container to initialize before starting health-retries countdown |
1154| `--health-start-interval` | Time between running the check during the start period |
1155| `--no-healthcheck` | Disable any container-specified `HEALTHCHECK` |
1156
1157Example:
1158
1159```console
1160$ docker run --name=test -d \
1161 --health-cmd='stat /etc/passwd || exit 1' \
1162 --health-interval=2s \
1163 busybox sleep 1d
1164$ sleep 2; docker inspect --format='{{.State.Health.Status}}' test
1165healthy
1166$ docker exec test rm /etc/passwd
1167$ sleep 2; docker inspect --format='{{json .State.Health}}' test
1168{
1169 "Status": "unhealthy",
1170 "FailingStreak": 3,
1171 "Log": [
1172 {
1173 "Start": "2016-05-25T17:22:04.635478668Z",
1174 "End": "2016-05-25T17:22:04.7272552Z",
1175 "ExitCode": 0,
1176 "Output": " File: /etc/passwd\n Size: 334 \tBlocks: 8 IO Block: 4096 regular file\nDevice: 32h/50d\tInode: 12 Links: 1\nAccess: (0664/-rw-rw-r--) Uid: ( 0/ root) Gid: ( 0/ root)\nAccess: 2015-12-05 22:05:32.000000000\nModify: 2015..."
1177 },
1178 {
1179 "Start": "2016-05-25T17:22:06.732900633Z",
1180 "End": "2016-05-25T17:22:06.822168935Z",
1181 "ExitCode": 0,
1182 "Output": " File: /etc/passwd\n Size: 334 \tBlocks: 8 IO Block: 4096 regular file\nDevice: 32h/50d\tInode: 12 Links: 1\nAccess: (0664/-rw-rw-r--) Uid: ( 0/ root) Gid: ( 0/ root)\nAccess: 2015-12-05 22:05:32.000000000\nModify: 2015..."
1183 },
1184 {
1185 "Start": "2016-05-25T17:22:08.823956535Z",
1186 "End": "2016-05-25T17:22:08.897359124Z",
1187 "ExitCode": 1,
1188 "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
1189 },
1190 {
1191 "Start": "2016-05-25T17:22:10.898802931Z",
1192 "End": "2016-05-25T17:22:10.969631866Z",
1193 "ExitCode": 1,
1194 "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
1195 },
1196 {
1197 "Start": "2016-05-25T17:22:12.971033523Z",
1198 "End": "2016-05-25T17:22:13.082015516Z",
1199 "ExitCode": 1,
1200 "Output": "stat: can't stat '/etc/passwd': No such file or directory\n"
1201 }
1202 ]
1203}
1204```
1205
1206The health status is also displayed in the `docker ps` output.
1207
1208### User
1209
1210The default user within a container is `root` (uid = 0). You can set a default
1211user to run the first process with the Dockerfile `USER` instruction. When
1212starting a container, you can override the `USER` instruction by passing the
1213`-u` option.
1214
1215```text
1216-u="", --user="": Sets the username or UID used and optionally the groupname or GID for the specified command.
1217```
1218
1219The followings examples are all valid:
1220
1221```text
1222--user=[ user | user:group | uid | uid:gid | user:gid | uid:group ]
1223```
1224
1225> **Note**
1226>
1227> If you pass a numeric user ID, it must be in the range of 0-2147483647. If
1228> you pass a username, the user must exist in the container.
1229
1230### Working directory
1231
1232The default working directory for running binaries within a container is the
1233root directory (`/`). The default working directory of an image is set using
1234the Dockerfile `WORKDIR` command. You can override the default working
1235directory for an image using the `-w` (or `--workdir`) flag for the `docker
1236run` command:
1237
1238```text
1239$ docker run --rm -w /my/workdir alpine pwd
1240/my/workdir
1241```
1242
1243If the directory doesn't already exist in the container, it's created.
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