path: root/docs/source/markdown/podman-build.1.md

% podman-build(1)

## NAME
podman\-build - Build a container image using a Containerfile

## SYNOPSIS
**podman build** [*options*] [*context*]

**podman image build** [*options*] [*context*]

## DESCRIPTION
**podman build** Builds an image using instructions from one or more
Containerfiles or Dockerfiles and a specified build context directory. A
Containerfile uses the same syntax as a Dockerfile internally. For this
document, a file referred to as a Containerfile can be a file named either
'Containerfile' or 'Dockerfile'.

The build context directory can be specified as the http(s) URL of an archive,
git repository or Containerfile.

If no context directory is specified, then Podman will assume the current
working directory as the build context, which should contain the Containerfile.

Containerfiles ending with a ".in" suffix will be preprocessed via CPP(1).  This
can be useful to decompose Containerfiles into several reusable parts that can
be used via CPP's **#include** directive.  Notice, a Containerfile.in file can
still be used by other tools when manually preprocessing them via `cpp -E`.

When the URL is an archive, the contents of the URL is downloaded to a temporary
location and extracted before execution.

When the URL is an Containerfile, the Containerfile is downloaded to a temporary
location.

When a Git repository is set as the URL, the repository is cloned locally and
then set as the context.

NOTE: `podman build` uses code sourced from the `buildah` project to build
container images.  This `buildah` code creates `buildah` containers for the
`RUN` options in container storage. In certain situations, when the
`podman build` crashes or users kill the `podman build` process, these external
containers can be left in container storage. Use the `podman ps --all --storage`
command to see these contaienrs. External containers can be removed with the
`podman rm --storage` command.

## OPTIONS

#### **--add-host**=*host*

Add a custom host-to-IP mapping (host:ip)

Add a line to /etc/hosts. The format is hostname:ip. The **--add-host** option
can be set multiple times.

#### **--annotation**=*annotation*

Add an image *annotation* (e.g. annotation=*value*) to the image metadata. Can
be used multiple times.

Note: this information is not present in Docker image formats, so it is
discarded when writing images in Docker formats.

#### **--arch**=*arch*

Set the ARCH of the image to the provided value instead of the architecture of
the host.

#### **--authfile**=*path*

Path of the authentication file. Default is
${XDG\_RUNTIME\_DIR}/containers/auth.json, which is set using `podman login`.
If the authorization state is not found there, $HOME/.docker/config.json is
checked, which is set using `docker login`.

Note: You can also override the default path of the authentication file by
setting the REGISTRY\_AUTH\_FILE environment variable.
`export REGISTRY_AUTH_FILE=path`

#### **--build-arg**=*arg=value*

Specifies a build argument and its value, which will be interpolated in
instructions read from the Containerfiles in the same way that environment
variables are, but which will not be added to environment variable list in the
resulting image's configuration.

#### **--cache-from**

Images to utilize as potential cache sources. Podman does not currently support
caching so this is a NOOP.

#### **--cap-add**=*CAP\_xxx*

When executing RUN instructions, run the command specified in the instruction
with the specified capability added to its capability set.
Certain capabilities are granted by default; this option can be used to add
more.

#### **--cap-drop**=*CAP\_xxx*

When executing RUN instructions, run the command specified in the instruction
with the specified capability removed from its capability set.
The CAP\_AUDIT\_WRITE, CAP\_CHOWN, CAP\_DAC\_OVERRIDE, CAP\_FOWNER,
CAP\_FSETID, CAP\_KILL, CAP\_MKNOD, CAP\_NET\_BIND\_SERVICE, CAP\_SETFCAP,
CAP\_SETGID, CAP\_SETPCAP, CAP\_SETUID, and CAP\_SYS\_CHROOT capabilities are
granted by default; this option can be used to remove them.

If a capability is specified to both the **--cap-add** and **--cap-drop**
options, it will be dropped, regardless of the order in which the options were
given.

#### **--cert-dir**=*path*

Use certificates at *path* (\*.crt, \*.cert, \*.key) to connect to the registry.
Default certificates directory is _/etc/containers/certs.d_. (Not available for
remote commands)

#### **--cgroup-parent**=*path*

Path to cgroups under which the cgroup for the container will be created. If the
path is not absolute, the path is considered to be relative to the cgroups path
of the init process. Cgroups will be created if they do not already exist.

#### **--compress**

This option is added to be aligned with other containers CLIs.
Podman doesn't communicate with a daemon or a remote server.
Thus, compressing the data before sending it is irrelevant to Podman.

#### **--cni-config-dir**=*directory*

Location of CNI configuration files which will dictate which plugins will be
used to configure network interfaces and routing for containers created for
handling `RUN` instructions, if those containers will be run in their own
network namespaces, and networking is not disabled.

#### **--cni-plugin-path**=*directory[:directory[:directory[...]]]*

List of directories in which the CNI plugins which will be used for configuring
network namespaces can be found.

#### **--cpu-period**=*limit*

Set the CPU period for the Completely Fair Scheduler (CFS), which is a
duration in microseconds. Once the container's CPU quota is used up, it will
not be scheduled to run until the current period ends. Defaults to 100000
microseconds.

On some systems, changing the CPU limits may not be allowed for non-root
users. For more details, see
https://github.com/containers/podman/blob/master/troubleshooting.md#26-running-containers-with-cpu-limits-fails-with-a-permissions-error

#### **--cpu-quota**=*limit*

Limit the CPU Completely Fair Scheduler (CFS) quota.

Limit the container's CPU usage. By default, containers run with the full
CPU resource. The limit is a number in microseconds. If you provide a number,
the container will be allowed to use that much CPU time until the CPU period
ends (controllable via **--cpu-period**).

On some systems, changing the CPU limits may not be allowed for non-root
users. For more details, see
https://github.com/containers/podman/blob/master/troubleshooting.md#26-running-containers-with-cpu-limits-fails-with-a-permissions-error

#### **--cpu-shares**, **-c**=*shares*

CPU shares (relative weight)

By default, all containers get the same proportion of CPU cycles. This
proportion can be modified by changing the container's CPU share weighting
relative to the weighting of all other running containers.

To modify the proportion from the default of 1024, use the **--cpu-shares**
flag to set the weighting to 2 or higher.

The proportion will only apply when CPU-intensive processes are 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

#### **--cpuset-cpus**=*num*

  CPUs in which to allow execution (0-3, 0,1)

#### **--cpuset-mems**=*nodes*

Memory nodes (MEMs) in which to allow execution (0-3, 0,1). Only effective on
NUMA systems.

If you have four memory nodes on your system (0-3), use `--cpuset-mems=0,1`
then processes in your container will only use memory from the first
two memory nodes.

#### **--creds**=*creds*

The [username[:password]] to use to authenticate with the registry if required.
If one or both values are not supplied, a command line prompt will appear and
the value can be entered.  The password is entered without echo.

#### **--decryption-key**=*key[:passphrase]*

The [key[:passphrase]] to be used for decryption of images. Key can point to
keys and/or certificates. Decryption will be tried with all keys. If the key is
protected by a passphrase, it is required to be passed in the argument and
omitted otherwise.

#### **--device**=_host-device_[**:**_container-device_][**:**_permissions_]

Add a host device to the container. Optional *permissions* parameter
can be used to specify device permissions, it is combination of
**r** for read, **w** for write, and **m** for **mknod**(2).

Example: **--device=/dev/sdc:/dev/xvdc:rwm**.

Note: if _host_device_ is a symbolic link then it will be resolved first.
The container will only store the major and minor numbers of the host device.

Note: if the user only has access rights via a group, accessing the device
from inside a rootless container will fail. The **crun**(1) runtime offers a
workaround for this by adding the option
#### **--annotation run.oci.keep_original_groups=1**.

#### **--disable-compression**, **-D**

Don't compress filesystem layers when building the image unless it is required
by the location where the image is being written.  This is the default setting,
because image layers are compressed automatically when they are pushed to
registries, and images being written to local storage would only need to be
decompressed again to be stored.  Compression can be forced in all cases by
specifying **--disable-compression=false**.

#### **--disable-content-trust**

This is a Docker specific option to disable image verification to a Docker
registry and is not supported by Podman.  This flag is a NOOP and provided
solely for scripting compatibility.

#### **--dns**=*dns*

Set custom DNS servers

This option can be used to override the DNS configuration passed to the
container. Typically this is necessary when the host DNS configuration is
invalid for the container (e.g., 127.0.0.1). When this is the case the `--dns`
flag is necessary for every run.

The special value **none** can be specified to disable creation of
/etc/resolv.conf in the container by Podman. The /etc/resolv.conf file in the
image will be used without changes.

#### **--dns-option**=*option*

Set custom DNS options

#### **--dns-search**=*domain*

Set custom DNS search domains

#### **--file**, **-f**=*Containerfile*

Specifies a Containerfile which contains instructions for building the image,
either a local file or an **http** or **https** URL.  If more than one
Containerfile is specified, *FROM* instructions will only be accepted from the
first specified file.

If a build context is not specified, and at least one Containerfile is a
local file, the directory in which it resides will be used as the build
context.

If you specify `-f -`, the Containerfile contents will be read from stdin.

#### **--force-rm**=*true|false*

Always remove intermediate containers after a build, even if the build fails
(default false).

#### **--format**

Control the format for the built image's manifest and configuration data.
Recognized formats include *oci* (OCI image-spec v1.0, the default) and
*docker* (version 2, using schema format 2 for the manifest).

Note: You can also override the default format by setting the BUILDAH\_FORMAT
environment variable.  `export BUILDAH_FORMAT=docker`

**-h**, **--help**

Print usage statement

#### **--http-proxy**

Pass through HTTP Proxy environment variables.

#### **--iidfile**=*ImageIDfile*

Write the image ID to the file.

#### **--ignorefile**

Path to an alternative .dockerignore file.

#### **--ipc**=*how*

Sets the configuration for IPC namespaces when handling `RUN` instructions.
The configured value can be "" (the empty string) or "container" to indicate
that a new IPC namespace should be created, or it can be "host" to indicate
that the IPC namespace in which `podman` itself is being run should be reused,
or it can be the path to an IPC namespace which is already in use by
another process.

#### **--isolation**=*type*

Controls what type of isolation is used for running processes as part of `RUN`
instructions.  Recognized types include *oci* (OCI-compatible runtime, the
default), *rootless* (OCI-compatible runtime invoked using a modified
configuration and its --rootless flag enabled, with *--no-new-keyring
--no-pivot* added to its *create* invocation, with network and UTS namespaces
disabled, and IPC, PID, and user namespaces enabled; the default for
unprivileged users), and *chroot* (an internal wrapper that leans more toward
chroot(1) than container technology).

Note: You can also override the default isolation type by setting the
BUILDAH\_ISOLATION environment variable.  `export BUILDAH_ISOLATION=oci`

#### **--jobs**=*number*

Run up to N concurrent stages in parallel.  If the number of jobs is greater
than 1, stdin will be read from /dev/null.  If 0 is specified, then there is
no limit in the number of jobs that run in parallel.

#### **--label**=*label*

Add an image *label* (e.g. label=*value*) to the image metadata. Can be used
multiple times.

Users can set a special LABEL **io.containers.capabilities=CAP1,CAP2,CAP3** in
a Containerfile that specified the list of Linux capabilities required for the
container to run properly. This label specified in a container image tells
Podman to run the container with just these capabilities. Podman launches the
container with just the specified capabilities, as long as this list of
capabilities is a subset of the default list.

If the specified capabilities are not in the default set, Podman will
print an error message and will run the container with the default capabilities.

#### **--layers**

Cache intermediate images during the build process (Default is `true`).

Note: You can also override the default value of layers by setting the
BUILDAH\_LAYERS environment variable. `export BUILDAH_LAYERS=true`

#### **--logfile**=*filename*

Log output which would be sent to standard output and standard error to the
specified file instead of to standard output and standard error.

#### **--loglevel**=*number*

Adjust the logging level up or down.  Valid option values range from -2 to 3,
with 3 being roughly equivalent to using the global *--debug* option, and
values below 0 omitting even error messages which accompany fatal errors.

#### **--memory**, **-m**=*LIMIT*
Memory limit (format: <number>[<unit>], where unit = b (bytes), k (kilobytes),
m (megabytes), or g (gigabytes))

Allows you to constrain the memory available to a container. If the host
supports swap memory, then the **-m** memory setting can be larger than physical
RAM. If a limit of 0 is specified (not using **-m**), the container's memory is
not limited. The actual limit may be rounded up to a multiple of the operating
system's page size (the value would be very large, that's millions of
trillions).

#### **--memory-swap**=*LIMIT*

A limit value equal to memory plus swap. Must be used with the  **-m**
(**--memory**) flag. The swap `LIMIT` should always be larger than **-m**
(**--memory**) value.  By default, the swap `LIMIT` will be set to double
the value of --memory.

The format of `LIMIT` is `<number>[<unit>]`. Unit can be `b` (bytes),
`k` (kilobytes), `m` (megabytes), or `g` (gigabytes). If you don't specify a
unit, `b` is used. Set LIMIT to `-1` to enable unlimited swap.

#### **--network**=*mode*, **--net**

Sets the configuration for network namespaces when handling `RUN` instructions.

Valid _mode_ values are:

- **none**: no networking.
- **host**: use the Podman host network stack. Note: the host mode gives the
container full access to local system services such as D-bus and is therefore
considered insecure.
- **ns:**_path_: path to a network namespace to join.
- **private**: create a new namespace for the container (default).

#### **--no-cache**

Do not use existing cached images for the container build. Build from the start
with a new set of cached layers.

#### **--os**=*string*

Set the OS to the provided value instead of the current operating system of the
host.

#### **--pid**=*pid*

Sets the configuration for PID namespaces when handling `RUN` instructions.
The configured value can be "" (the empty string) or "container" to indicate
that a new PID namespace should be created, or it can be "host" to indicate
that the PID namespace in which `podman` itself is being run should be reused,
or it can be the path to a PID namespace which is already in use by another
process.

#### **--platform**="Linux"

This option has no effect on the build. Other container engines use this option
to control the execution platform for the build (e.g., Windows, Linux) which is
not required for Buildah as it supports only Linux.

#### **--pull**

When the option is specified or set to "true", pull the image from the first
registry it is found in as listed in registries.conf.  Raise an error if not
found in the registries, even if the image is present locally.

If the option is disabled (with *--pull=false*) or not specified, pull the
image from the registry only if the image is not present locally. Raise an
error if the image is not found in the registries and is not present locally.

#### **--pull-always**

Pull the image from the first registry it is found in as listed in
registries.conf. Raise an error if not found in the registries, even if the
image is present locally.

#### **--pull-never**

Do not pull the image from the registry, use only the local version. Raise an
error if the image is not present locally.

#### **--quiet**, **-q**

Suppress output messages which indicate which instruction is being processed,
and of progress when pulling images from a registry, and when writing the
output image.

#### **--rm**=*true|false*

Remove intermediate containers after a successful build (default true).

#### **--runtime**=*path*

The *path* to an alternate OCI-compatible runtime, which will be used to run
commands specified by the **RUN** instruction.

Note: You can also override the default runtime by setting the BUILDAH\_RUNTIME
environment variable.  `export BUILDAH_RUNTIME=/usr/local/bin/runc`

#### **--security-opt**=*option*

Security Options

- `apparmor=unconfined` : Turn off apparmor confinement for the container
- `apparmor=your-profile` : Set the apparmor confinement profile for the
container

- `label=user:USER`     : Set the label user for the container processes
- `label=role:ROLE`     : Set the label role for the container processes
- `label=type:TYPE`     : Set the label process type for the container processes
- `label=level:LEVEL`   : Set the label level for the container processes
- `label=filetype:TYPE` : Set the label file type for the container files
- `label=disable`       : Turn off label separation for the container
- `no-new-privileges`   : Not supported

- `seccomp=unconfined` : Turn off seccomp confinement for the container
- `seccomp=profile.json` :  White listed syscalls seccomp Json file to be used
as a seccomp filter

#### **--shm-size**=*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`.

#### **--sign-by**=*fingerprint*

Sign the image using a GPG key with the specified FINGERPRINT.

#### **--squash**

Squash all of the image's new layers into a single new layer; any preexisting
layers are not squashed.

#### **--squash-all**

Squash all of the new image's layers (including those inherited from a base
image) into a single new layer.

#### **--tag**, **-t**=*imageName*

Specifies the name which will be assigned to the resulting image if the build
process completes successfully.
If _imageName_ does not include a registry name, the registry name *localhost*
will be prepended to the image name.

#### **--target**=*stageName*

Set the target build stage to build.  When building a Containerfile with
multiple build stages, --target can be used to specify an intermediate build
stage by name as the final stage for the resulting image. Commands after the target stage will be skipped.

#### **--timestamp** *seconds*

Set the create timestamp to seconds since epoch to allow for deterministic
builds (defaults to current time). By default, the created timestamp is changed
and written into the image manifest with every commit, causing the image's
sha256 hash to be different even if the sources are exactly the same otherwise.
When --timestamp is set, the created timestamp is always set to the time
specified and therefore not changed, allowing the image's sha256 hash to remain the
same. All files committed to the layers of the image will be created with the
timestamp.

#### **--tls-verify**=*true|false*

Require HTTPS and verify certificates when talking to container registries
(defaults to true).

#### **--ulimit**=*type*=*soft-limit*[:*hard-limit*]

Specifies resource limits to apply to processes launched when processing `RUN`
instructions. This option can be specified multiple times.  Recognized resource
types include:
  "core": maximum core dump size (ulimit -c)
  "cpu": maximum CPU time (ulimit -t)
  "data": maximum size of a process's data segment (ulimit -d)
  "fsize": maximum size of new files (ulimit -f)
  "locks": maximum number of file locks (ulimit -x)
  "memlock": maximum amount of locked memory (ulimit -l)
  "msgqueue": maximum amount of data in message queues (ulimit -q)
  "nice": niceness adjustment (nice -n, ulimit -e)
  "nofile": maximum number of open files (ulimit -n)
  "nproc": maximum number of processes (ulimit -u)
  "rss": maximum size of a process's (ulimit -m)
  "rtprio": maximum real-time scheduling priority (ulimit -r)
  "rttime": maximum amount of real-time execution between blocking syscalls
  "sigpending": maximum number of pending signals (ulimit -i)
  "stack": maximum stack size (ulimit -s)

#### **--userns**=*how*

Sets the configuration for user namespaces when handling `RUN` instructions.
The configured value can be "" (the empty string) or "container" to indicate
that a new user namespace should be created, it can be "host" to indicate that
the user namespace in which `podman` itself is being run should be reused, or
it can be the path to an user namespace which is already in use by another
process.

#### **--userns-uid-map**=*mapping*

Directly specifies a UID mapping which should be used to set ownership, at the
filesystem level, on the working container's contents.
Commands run when handling `RUN` instructions will default to being run in
their own user namespaces, configured using the UID and GID maps.

Entries in this map take the form of one or more triples of a starting
in-container UID, a corresponding starting host-level UID, and the number of
consecutive IDs which the map entry represents.

This option overrides the *remap-uids* setting in the *options* section of
/etc/containers/storage.conf.

If this option is not specified, but a global --userns-uid-map setting is
supplied, settings from the global option will be used.

If none of --userns-uid-map-user, --userns-gid-map-group, or --userns-uid-map
are specified, but --userns-gid-map is specified, the UID map will be set to
use the same numeric values as the GID map.

#### **--userns-gid-map**=*mapping*

Directly specifies a GID mapping which should be used to set ownership, at the
filesystem level, on the working container's contents.
Commands run when handling `RUN` instructions will default to being run in
their own user namespaces, configured using the UID and GID maps.

Entries in this map take the form of one or more triples of a starting
in-container GID, a corresponding starting host-level GID, and the number of
consecutive IDs which the map entry represents.

This option overrides the *remap-gids* setting in the *options* section of
/etc/containers/storage.conf.

If this option is not specified, but a global --userns-gid-map setting is
supplied, settings from the global option will be used.

If none of --userns-uid-map-user, --userns-gid-map-group, or --userns-gid-map
are specified, but --userns-uid-map is specified, the GID map will be set to
use the same numeric values as the UID map.

#### **--userns-uid-map-user**=*user*

Specifies that a UID mapping which should be used to set ownership, at the
filesystem level, on the working container's contents, can be found in entries
in the `/etc/subuid` file which correspond to the specified user.
Commands run when handling `RUN` instructions will default to being run in
their own user namespaces, configured using the UID and GID maps.
If --userns-gid-map-group is specified, but --userns-uid-map-user is not
specified, `podman` will assume that the specified group name is also a
suitable user name to use as the default setting for this option.

#### **--userns-gid-map-group**=*group*

Specifies that a GID mapping which should be used to set ownership, at the
filesystem level, on the working container's contents, can be found in entries
in the `/etc/subgid` file which correspond to the specified group.
Commands run when handling `RUN` instructions will default to being run in
their own user namespaces, configured using the UID and GID maps.
If --userns-uid-map-user is specified, but --userns-gid-map-group is not
specified, `podman` will assume that the specified user name is also a
suitable group name to use as the default setting for this option.

#### **--uts**=*how*

Sets the configuration for UTS namespaces when the handling `RUN` instructions.
The configured value can be "" (the empty string) or "container" to indicate
that a new UTS namespace should be created, or it can be "host" to indicate
that the UTS namespace in which `podman` itself is being run should be reused,
or it can be the path to a UTS namespace which is already in use by another
process.

#### **--volume**, **-v**[=*[HOST-DIR:CONTAINER-DIR[:OPTIONS]]*]

   Create a bind mount. If you specify, ` -v /HOST-DIR:/CONTAINER-DIR`, Podman
   bind mounts `/HOST-DIR` in the host to `/CONTAINER-DIR` in the Podman
   container. The `OPTIONS` are a comma delimited list and can be: <sup>[[1]](#Footnote1)</sup>

   * [rw|ro]
   * [z|Z|O]
   * [`[r]shared`|`[r]slave`|`[r]private`]

The `CONTAINER-DIR` must be an absolute path such as `/src/docs`. The `HOST-DIR`
must be an absolute path as well. Podman bind-mounts the `HOST-DIR` to the
path you specify. For example, if you supply `/foo` as the host path,
Podman copies the contents of `/foo` to the container filesystem on the host
and bind mounts that into the container.

You can specify multiple  **-v** options to mount one or more mounts to a
container.

You can add the `:ro` or `:rw` suffix to a volume to mount it read-only or
read-write mode, respectively. By default, the volumes are mounted read-write.
See examples.

  `Labeling Volume Mounts`

Labeling systems like SELinux require that proper labels are placed on volume
content mounted into a container. Without a label, the security system might
prevent the processes running inside the container from using the content. By
default, Podman does not change the labels set by the OS.

To change a label in the container context, you can add either of two suffixes
`:z` or `:Z` to the volume mount. These suffixes tell Podman to relabel file
objects on the shared volumes. The `z` option tells Podman that two containers
share the volume content. As a result, Podman labels the content with a shared
content label. Shared volume labels allow all containers to read/write content.
The `Z` option tells Podman to label the content with a private unshared label.
Only the current container can use a private volume.

  `Overlay Volume Mounts`

   The `:O` flag tells Podman to mount the directory from the host as a
temporary storage using the Overlay file system. The `RUN` command containers
are allowed to modify contents within the mountpoint and are stored in the
container storage in a separate directory.  In Overlay FS terms the source
directory will be the lower, and the container storage directory will be the
upper. Modifications to the mount point are destroyed when the `RUN` command
finishes executing, similar to a tmpfs mount point.

  Any subsequent execution of `RUN` commands sees the original source directory
content, any changes from previous RUN commands no longer exists.

  One use case of the `overlay` mount is sharing the package cache from the
host into the container to allow speeding up builds.

  Note:

     - Overlay mounts are not currently supported in rootless mode.
     - The `O` flag is not allowed to be specified with the `Z` or `z` flags.
Content mounted into the container is labeled with the private label.
       On SELinux systems, labels in the source directory needs to be readable
by the container label. If not, SELinux container separation must be disabled
for the container to work.
     - Modification of the directory volume mounted into the container with an
overlay mount can cause unexpected failures.  It is recommended that you do not
modify the directory until the container finishes running.

By default bind mounted volumes are `private`. That means any mounts done
inside containers will not be visible on the host and vice versa. This behavior
can be changed by specifying a volume mount propagation property.

When the mount propagation policy is set to `shared`, any mounts completed
inside the container on that volume will be visible to both the host and
container. When the mount propagation policy is set to `slave`, one way mount
propagation is enabled and any mounts completed on the host for that volume will
be visible only inside of the container. To control the mount propagation
property of volume use the `:[r]shared`, `:[r]slave` or `:[r]private`
propagation flag. The propagation property can be specified only for bind mounted
volumes and not for internal volumes or named volumes. For mount propagation to
work on the source mount point (mount point where source dir is mounted on) has
to have the right propagation properties. For shared volumes, the source mount
point has to be shared. And for slave volumes, the source mount has to be either
shared or slave. <sup>[[1]](#Footnote1)</sup>

Use `df <source-dir>` to determine the source mount and then use
`findmnt -o TARGET,PROPAGATION <source-mount-dir>` to determine propagation
properties of source mount, if `findmnt` utility is not available, the source
mount point can be determined by looking at the mount entry in
`/proc/self/mountinfo`. Look at `optional fields` and see if any propagation
properties are specified.
`shared:X` means the mount is `shared`, `master:X` means the mount is `slave`
and if nothing is there that means the mount is `private`. <sup>[[1]](#Footnote1)</sup>

To change propagation properties of a mount point use the `mount` command. For
example, to bind mount the source directory `/foo` do
`mount --bind /foo /foo` and `mount --make-private --make-shared /foo`. This
will convert /foo into a `shared` mount point.  The propagation properties of
the source mount can be changed directly. For instance if `/` is the source
mount for `/foo`, then use `mount --make-shared /` to convert `/` into a
`shared` mount.

## EXAMPLES

### Build an image using local Containerfiles

```
$ podman build .

$ podman build -f Containerfile.simple .

$ cat $HOME/Dockerfile | podman build -f - .

$ podman build -f Dockerfile.simple -f Containerfile.notsosimple .

$ podman build -f Dockerfile.in $HOME

$ podman build -t imageName .

$ podman build --tls-verify=true -t imageName -f Dockerfile.simple .

$ podman build --tls-verify=false -t imageName .

$ podman build --runtime-flag log-format=json .

$ podman build --runtime-flag debug .

$ podman build --authfile /tmp/auths/myauths.json --cert-dir $HOME/auth --tls-verify=true --creds=username:password -t imageName -f Dockerfile.simple .

$ podman build --memory 40m --cpu-period 10000 --cpu-quota 50000 --ulimit nofile=1024:1028 -t imageName .

$ podman build --security-opt label=level:s0:c100,c200 --cgroup-parent /path/to/cgroup/parent -t imageName .

$ podman build --volume /home/test:/myvol:ro,Z -t imageName .

$ podman build -v /var/lib/yum:/var/lib/yum:O -t imageName .

$ podman build --layers -t imageName .

$ podman build --no-cache -t imageName .

$ podman build --layers --force-rm -t imageName .

$ podman build --no-cache --rm=false -t imageName .
```

### Building an image using a URL, Git repo, or archive

  The build context directory can be specified as a URL to a Containerfile, a
Git repository, or URL to an archive. If the URL is a Containerfile, it is
downloaded to a temporary location and used as the context. When a Git
repository is set as the URL, the repository is cloned locally to a temporary
location and then used as the context. Lastly, if the URL is an archive, it is
downloaded to a temporary location and extracted before being used as the
context.

#### Building an image using a URL to a Containerfile

  Podman will download the Containerfile to a temporary location and then use
it as the build context.

```
$ podman build https://10.10.10.1/podman/Containerfile
```

#### Building an image using a Git repository

  Podman will clone the specified GitHub repository to a temporary location and
use it as the context. The Containerfile at the root of the repository will be
used and it only works if the GitHub repository is a dedicated repository.

```
$ podman build git://github.com/scollier/purpletest
```

#### Building an image using a URL to an archive

  Podman will fetch the archive file, decompress it, and use its contents as the
build context. The Containerfile at the root of the archive and the rest of the
archive will get used as the context of the build. If you pass
`-f PATH/Containerfile` option as well, the system will look for that file
inside the contents of the archive.

```
$ podman build -f dev/Containerfile https://10.10.10.1/podman/context.tar.gz
```

  Note: supported compression formats are 'xz', 'bzip2', 'gzip' and 'identity'
(no compression).

## Files

### `.dockerignore`

If the file .dockerignore exists in the context directory, `buildah copy` reads
its contents. Use the `--ignorefile` flag to override .dockerignore path location.
Podman uses the content to exclude files and directories from the context
directory, when executing COPY and ADD directives in the
Containerfile/Dockerfile

Users can specify a series of Unix shell globals in a .dockerignore file to
identify files/directories to exclude.

Podman supports a special wildcard string `**` which matches any number of
directories (including zero). For example, **/*.go will exclude all files that
end with .go that are found in all directories.

Example .dockerignore file:

```
# exclude this content for image
*/*.c
**/output*
src
```

`*/*.c`
Excludes files and directories whose names ends with .c in any top level
subdirectory. For example, the source file include/rootless.c.

`**/output*`
Excludes files and directories starting with `output` from any directory.

`src`
Excludes files named src and the directory src as well as any content in it.

Lines starting with ! (exclamation mark) can be used to make exceptions to
exclusions. The following is an example .dockerignore file that uses this
mechanism:
```
*.doc
!Help.doc
```

Exclude all doc files except Help.doc from the image.

This functionality is compatible with the handling of .dockerignore files
described here:

https://docs.docker.com/engine/reference/builder/#dockerignore-file

**registries.conf** (`/etc/containers/registries.conf`)

registries.conf is the configuration file which specifies which container
registries should be consulted when completing image names which do not include
a registry or domain portion.

## Troubleshooting

### lastlog sparse file

If you are using a useradd command within a Containerfile with a large UID/GID,
it will create a large sparse file `/var/log/lastlog`.  This can cause the
build to hang forever.  Go language does not support sparse files correctly,
which can lead to some huge files being created in your container image.

If you are using `useradd` within your build script, you should pass the
`--no-log-init or -l` option to the `useradd` command.  This option tells
useradd to stop creating the lastlog file.

## SEE ALSO
podman(1), buildah(1), containers-registries.conf(5), crun(8), runc(8), useradd(8), podman-ps(1), podman-rm(1)

## HISTORY
Aug 2020, Additional options and .dockerignore added by Dan Walsh <dwalsh@redhat.com>

May 2018, Minor revisions added by Joe Doss <joe@solidadmin.com>

December 2017, Originally compiled by Tom Sweeney <tsweeney@redhat.com>

## FOOTNOTES
<a name="Footnote1">1</a>: The Podman project is committed to inclusivity, a
core value of open source. The `master` and `slave` mount propagation
terminology used here is problematic and divisive, and should be changed.
However, these terms are currently used within the Linux kernel and must be
used as-is at this time. When the kernel maintainers rectify this usage,
Podman will follow suit immediately.