Bind Paths and Mounts¶
If enabled by the system administrator, Singularity allows you to map directories on your host system to directories within your container using bind mounts. This allows you to read and write data on the host system with ease.
When Singularity ‘swaps’ the host operating system for the one inside your container, the host file systems becomes inaccessible. But you may want to read and write files on the host system from within the container. To enable this functionality, Singularity will bind directories back into the container via two primary methods: system-defined bind paths and user-defined bind paths.
System-defined bind paths¶
The system administrator has the ability to define what bind paths will be
included automatically inside each container. Some bind paths are automatically
derived (e.g. a user’s home directory) and some are statically defined (e.g.
bind paths in the Singularity configuration file). In the default
configuration, the directories
$PWD are among the system-defined bind paths.
User-defined bind paths¶
If the system administrator has enabled user control of binds, you will be able to request your own bind paths within your container.
The Singularity action commands (
instance start will accept the
--bind/-B command-line option to specify
bind paths, and will also honor the
$SINGULARITY_BINDPATH) environment variable. The argument for this option is
a comma-delimited string of bind path specifications in the format
dest are paths outside and inside
of the container respectively. If
dest is not given, it is set equal to
src. Mount options (
opts) may be specified as
ro (read-only) or
rw (read/write, which is the default). The
--bind/-B option can be
specified multiple times, or a comma-delimited string of bind path
specifications can be used.
Specifying bind paths¶
Here’s an example of using the
--bind option and binding
/data on the
/mnt in the container (
/mnt does not need to already exist in
$ ls /data bar foo $ singularity exec --bind /data:/mnt my_container.sif ls /mnt bar foo
You can bind multiple directories in a single command with this syntax:
$ singularity shell --bind /opt,/data:/mnt my_container.sif
This will bind
/opt on the host to
/opt in the container and
on the host to
/mnt in the container.
Using the environment variable instead of the command line argument, this would be:
$ export SINGULARITY_BIND="/opt,/data:/mnt" $ singularity shell my_container.sif
Using the environment variable
$SINGULARITY_BIND, you can bind paths even
when you are running your container as an executable file with a runscript. If
you bind many directories into your Singularity containers and they don’t
change, you could even benefit by setting this variable in your
A note on using
--bind with the
To mount a bind path inside the container, a bind point must be defined within the container. The bind point is a directory within the container that Singularity can use as a destination to bind a directory on the host system.
Starting in version 3.0, Singularity will do its best to bind mount requested paths into a container regardless of whether the appropriate bind point exists within the container. Singularity can often carry out this operation even in the absence of the “overlay fs” feature.
However, binding paths to non-existent points within the container can result in
unexpected behavior when used in conjuction with the
--writable flag, and is
therefore disallowed. If you need to specify bind paths in combination with the
--writable flag, please ensure that the appropriate bind points exist within
the container. If they do not already exist, it will be necessary to modify the
container and create them.