You may wish to customize your build environment by doing things such as specifying a custom cache directory for images, or sending your Docker Credentials to the registry endpoint. In this section, we will discuss these and other topics related to the build environment.
Apptainer will cache SIF container images generated from remote
sources, and any OCI/docker layers used to create them. The cache is
$HOME/.apptainer/cache by default. The location of the
cache can be changed by setting the
If you run builds as root, using
sudo, images will be cached in root’s home
/root, rather than your user’s home directory. If you have set
APPTAINER_CACHEDIR environment variable, you may use
option to pass the value of
APPTAINER_CACHEDIR through to the root user’s
environment. This allows you to control where images will be cached even when
running builds under
$ export APPTAINER_CACHEDIR=/tmp/user/temporary-cache # Running a build under your user account $ apptainer build --fakeroot myimage.sif mydef.def # Running a build with sudo, must use -E to pass env var $ sudo -E apptainer build myimage.sif mydef.def
If you change the value of
APPTAINER_CACHEDIR be sure to choose a
location that is:
Unique to you. Permissions are set on the cache so that private images cached for one user are not exposed to another. This means that Apptainer cache directories cannot be shared across users.
Located on a filesystem with sufficient space for the number and size of container images you anticipate using.
Located on a filesystem that supports atomic rename, if possible.
If you are not certain that your
filesystems support atomic rename, do not run Apptainer in parallel using
remote container URLs. Instead, use
apptainer pull to create a local
SIF image, and then run this SIF image in a parallel step. Alternatively, you
may use the
--disable-cache option, but this will result in each
Apptainer instance independently fetching the container from the remote
source, into a temporary location.
Inside the cache location you will find separate directories for the different kinds of data that are cached:
$HOME/.apptainer/cache/blob $HOME/.apptainer/cache/library $HOME/.apptainer/cache/net $HOME/.apptainer/cache/oci-tmp $HOME/.apptainer/cache/shub
You can safely delete these directories, or content within them. Apptainer will re-create any directories and data that are needed in future runs.
You should not add any additional files, or modify files in the cache, as this
may cause checksum / integrity errors when you run or build containers. If you
experience problems use,
apptainer cache clean to reset the cache to a
clean, empty state.
BoltDB Corruption Errors
The library that Apptainer uses to retrieve and cache Docker/OCI layers keeps track of them using a single-file database. If your home directory is on a network filesystem which experiences interruptions, or you run out of storage, it is possible for this database to become inconsistent.
If you observe error messages that mention github.com/etcd-io/bbolt when trying to run Apptainer, then you should remove the database file:
cache command for Apptainer allows you to view and clean up your
cache, without needing to manually inspect the cache directories.
If you have built images as root, directly or via
sudo, the default cache
location for those builds is
/root/.apptainer. You will need to use
sudo when running
cache clean or
cache list to manage these cache
Listing the Cache
To view a summary of cache usage, use
apptainer cache list:
$ apptainer cache list There are 4 container file(s) using 59.45 MB and 23 oci blob file(s) using 379.10 MB of space Total space used: 438.55 MB
To view more detailed information, use
apptainer cache list -v:
$ apptainer cache list -v NAME DATE CREATED SIZE TYPE 0ed5a98249068fe0592edb 2020-05-27 12:57:22 192.21 MB blob 1d9cd1b99a7eca56d8f2be 2020-05-28 15:19:07 0.35 kB blob 219c332183ec3800bdfda4 2020-05-28 12:22:13 0.35 kB blob 2adae3950d4d0f11875568 2020-05-27 12:57:16 51.83 MB blob 376057ac6fa17f65688c56 2020-05-27 12:57:12 50.39 MB blob 496548a8c952b37bdf149a 2020-05-27 12:57:14 10.00 MB blob 5a63a0a859d859478f3046 2020-05-27 12:57:13 7.81 MB blob 5efaeecfa72afde779c946 2020-05-27 12:57:25 0.23 kB blob 6154df8ff9882934dc5bf2 2020-05-27 08:37:22 0.85 kB blob 70d0b3967cd8abe96c9719 2020-05-27 12:57:24 26.61 MB blob 8f5af4048c33630473b396 2020-05-28 15:19:07 0.57 kB blob 95c3f3755f37380edb2f8f 2020-05-28 14:07:20 2.48 kB blob 96878229af8adf91bcbf11 2020-05-28 14:07:20 0.81 kB blob af88fdb253aac46693de78 2020-05-28 12:22:13 0.58 kB blob bb94ffe723890b4d62d742 2020-05-27 12:57:23 6.15 MB blob c080bf936f6a1fdd2045e3 2020-05-27 12:57:25 1.61 kB blob cbdbe7a5bc2a134ca8ec91 2020-05-28 12:22:13 2.81 MB blob d51af753c3d3a984351448 2020-05-27 08:37:21 28.56 MB blob d9cbbca60e5f0fc028b13c 2020-05-28 15:19:06 760.85 kB blob db8816f445487e48e1d614 2020-05-27 12:57:25 1.93 MB blob fc878cd0a91c7bece56f66 2020-05-27 08:37:22 32.30 kB blob fee5db0ff82f7aa5ace634 2020-05-27 08:37:22 0.16 kB blob ff110406d51ca9ea722112 2020-05-27 12:57:25 7.78 kB blob sha256.02ee8bf9dc335c2 2020-05-29 13:45:14 28.11 MB library sha256.5111f59250ac94f 2020-05-28 13:14:39 782.34 kB library 747d2dbbaaee995098c979 2020-05-28 14:07:22 27.77 MB oci-tmp 9a839e63dad54c3a6d1834 2020-05-28 12:22:13 2.78 MB oci-tmp There are 4 container file(s) using 59.45 MB and 23 oci blob file(s) using 379.10 MB of space Total space used: 438.55 MB
All cache entries are named using a content hash, so that identical layers or images that are pulled from different URIs do not result in duplication within the cache.
blob are OCI/docker layers and manifests, which are used to
create SIF format images in the
oci-tmp cache. Other caches are named for
the source of the image, e.g.
You can limit the cache list to a specific cache type with the
Cleaning the Cache
To reclaim space used by the Apptainer cache, use
apptainer cache clean will remove all cache entries,
after asking you to confirm:
$ apptainer cache clean This will delete everything in your cache (containers from all sources and OCI blobs). Hint: You can see exactly what would be deleted by canceling and using the --dry-run option. Do you want to continue? [N/y] n
-n option to see the files that would be
deleted, or the
-f option to clean without asking for
If you want to leave your most recent cached images in place, but remove
images that were cached longer ago, you can use the
option. E.g. to clean cache entries older than 30 days:
$ apptainer cache clean --days 30
To remove only a specific kind of cache entry, e.g. only library images,
$ apptainer cache clean --type library
When building a container, or pulling/running an Apptainer container from a Docker/OCI source, a temporary working space is required. The container is constructed in this temporary space before being packaged into an Apptainer SIF image.
The location for temporary directories defaults to
However, Apptainer will respect the environment variable
both of these locations can be overridden by setting the environment
The temporary directory used during a build must be on a filesystem that has
enough space to hold the entire container image, uncompressed, including any
temporary files that are created and later removed in the course of the build.
You may therefore need to set
APPTAINER_TMPDIR when building a large
container on a system which has a small
Remember to use
-E option to pass the value of
through to root’s environment when executing the
build command with
Many modern Linux distributions use an in-memory
/tmp when installed on a computer with a sufficient amount of
RAM. This may limit the size of container you can build, as temporary
/tmp share RAM with runniing programs etc. A
tmpfs also uses default mount options that can interfere with
some container builds.
If you experience problems, set
APPTAINER_TMPDIR to a disk location, or
/tmp mount on your system.
With Apptainer it is possible to build and run encrypted containers. The containers are decrypted at runtime entirely in memory, meaning that no intermediate decrypted data is ever present on disk. See encrypted containers for more details.
If a flag is represented by both a CLI option and an environment variable, and both are set, the CLI option will take precedence. This is true for all environment variables with the exception for
APPTAINER_BINDPATH, which are combined with the
--bindoption / argument pair, if both are present.
Environment variables will override default values of CLI options that have not been explicitly set in the command line.
Any default values for CLI options that have not been overridden on the command line, or by corresponding environment variables, will then take effect.
The following variables have defaults that can be overridden by assigning your own values to the corresponding environment variables at runtime:
Set this to login to a Docker Repository interactively.
Your Docker username.
Your Docker password.
Is not obtained from the environment, but is a hard coded default
(“/bin/bash”). This is the fallback command used in the case that the docker
image does not have a CMD or ENTRYPOINT.
Is the default tag,
This is relevant if you want to use a registry that doesn’t support https. A
typical use-case for this variable is when using local registry, running on
the same machine as Apptainer itself.
Used to specify the library to pull from.
Default is the currently selected remote endpoint.
Used to pass a plaintext passphrase to be used to encrypt a container file
system (in conjunction with the
--encrypt flag). The default is empty.
Used to specify the location of a public key to use for container encryption
(in conjunction with the
--encrypt flag). The default is empty.