conda-pack can package environments into SquashFS, a compressed, read-only Linux filesystem. These filesystems can then be mounted directly, without decompressing them first. This allows using packed environments immediately and without consuming disk space.


Packing environments into SquashFS works on MacOS and Linux. You will need to install squashfs-tools, more specifically the mksquashfs command. On Ubuntu run apt-get install squashfs-tools, on MacOS brew install squashfs or alternatively (Linux+MacOS) install from conda-forge through conda install -c conda-forge squashfs-tools.


Mounting SquashFS environments is only possible on MacOS and Linux.

On Linux there are two ways:

  • Mounting directly: Since SquashFS is part of the Linux kernel, it can be mounted using mount -t squashfs <filename> <mountpoint>. This will require root or CAP_SYS_ADMIN.

  • Mounting as Filesystem in Userspace (FUSE): This can be done by installing squashfuse, for example through apt-get install squashfuse (Ubuntu), conda install -c conda-forge squashfuse or from source. Contrary to the Kernel-version of SquashFS, squashfuse doesn’t require root permissions to run. squashfuse_ll comes packaged with squashfuse and is often faster.

On Mac only the FUSE option is available:

  • First install macFUSE, eg via brew install --cask macfuse.

  • Then install squashfuse, ideally from source.

Python Example

Create an environment:

$ conda create -y -n example python=3.9 numpy pandas scikit-learn

Pack the environment into SquashFS:

$ conda pack -n example --format squashfs --n-threads 4

Create a directory to mount to:

$ mkdir env_mountpoint

Option 1 (Linux + MacOS): Mount the environment using squashfuse:

$ squashfuse example.squashfs env_mountpoint

Option 2 (Linux): Mount the environment using mount:

$ sudo mount -t squashfs example.squashfs env_mountpoint

Compression options

Compression can be specified through --compress-level. Default is level 4, which will use zstd compression.

When selecting a compression option for packing, keep in mind the kernel or squashfuse version on the target system. For older systems, make sure that SquashFS or squashfuse support zstd compression (Linux kernel version >=4.14 or squashfuse >= 0.1.101). If zstd isn’t supported on the target, you can always compress with xz instead.

  • 0: no compression

  • 1-8: zstd with increasing compression level

  • 9: xz

Making the unpacked environment writeable

SquashFS is a read-only filesystem. Sometimes the unpacked environment needs to be writeable on the target machine, for example to install more packages. A good way to do this is to use Union mounting to add a writeable layer on top of the read-only SquashFS. On Linux the most used option is OverlayFS.

To set this up, we create three layers:

  1. The SquashFS-packed conda env as a read-only lower layer

  2. A writeable working directory, necessary for OverlayFS

  3. A writeable upper directory, where all new and changed files will go

$ # 1. Create read-only lower layer, consisting of squashFS-packed conda env
$ mkdir squashFS_mountpoint
$ sudo mount -t squashfs example.squashfs squashFS_mountpoint
$ # 2. Create workdir & 3. Create upperdir
$ mkdir workdir upperdir

Now we combine them into a single directory writeable_env, which will contain our environment but which will be writeable.

$ mkdir writeable_env
$ sudo mount -t overlay overlay \
    -o lowerdir=squashFS_mountpoint,upperdir=upperdir,workdir=workdir writeable_env

Any files created in the writeable_env directory will also show up in upperdir. After unmounting, delete upperdir and workdir and all changes made to the environment will be gone.