Singularity Configuration Files

As a Singularity Administrator, you will have access to various configuration files, that will let you manage container resources, set security restrictions and configure network options etc, when installing Singularity across the system. All these files can be found in /usr/local/etc/singularity by default (though its location will obviously differ based on options passed during the installation). This page will describe the following configuration files and the various parameters contained by them. They are usually self documenting but here are several things to pay special attention to:


Most of the configuration options are set using the file singularity.conf that defines the global configuration for Singularity across the entire system. Using this file, system administrators can have direct say as to what functions the users can utilize. As a security measure, it must be owned by root and must not be writable by users or Singularity will refuse to run.

The following are some of the configurable options:

ALLOW SETUID: To use containers, your users will have to have access to some privileged system calls. One way singularity achieves this is by using binaries with the setuid bit enabled. This variable lets you enable/disable users ability to utilize these binaries within Singularity. By default, it is set to “Yes”, but when disabled, various Singularity features will not function (e.g. mounting of the Singularity image file format).

USER BIND CONTROL: This allows admins to enable/disable users to define bind points at runtime. By Default, its “YES”, which means users can specify bind points, scratch and tmp locations.

BIND PATH: Used for setting of automatic bind points entries. You can define a list of files/directories that should be made available from within the container. If the file exists within the container on which to attach to use the path like:

bind path = /etc/localtime

You can specify different source and destination locations using:

bind path = /etc/singularity/default-nsswitch.conf:/etc/nsswitch.conf

MOUNT DEV: Should be set to “YES”, if you want to automatically bind mount /dev within the container. If set to ‘minimal’, then only ‘null’, ‘zero’, ‘random’, ‘urandom’, and ‘shm’ will be included.

MOUNT HOME: To automatically determine the calling of user’s home directory and attempt to mount it’s base path into the container.

Limiting containers

There are several ways in which you can limit the running of containers in your system:

LIMIT CONTAINER OWNERS: Only allow containers to be used that are owned by a given user.

LIMIT CONTAINER GROUPS: Only allow containers to be used that are owned by a given group.

LIMIT CONTAINER PATHS: Only allow containers to be used that are located within an allowed path prefix.


These features will only apply when Singularity is running in SUID mode and the user is non-root. By default they all are set to NULL.

The singularity.conf file is well documented and most information can be gleaned by consulting it directly.


Cgroups or Control groups let you implement metering and limiting on the resources used by processes. You can limit memory, CPU. You can block IO, network IO, set SEL permissions for device nodes etc.


The --apply-cgroups option can only be used with root privileges.


When you are limiting resources, apply the settings in the TOML file by using the path as an argument to the --apply-cgroups option like so:

$ sudo singularity shell --apply-cgroups /path/to/cgroups.toml my_container.sif

Limiting memory

To limit the amount of memory that your container uses to 500MB (524288000 bytes):

    limit = 524288000

Start your container like so:

$ sudo singularity instance start --apply-cgroups path/to/cgroups.toml my_container.sif instance1

After that, you can verify that the container is only using 500MB of memory. (This example assumes that instance1 is the only running instance.)

$ cat /sys/fs/cgroup/memory/singularity/*/memory.limit_in_bytes

Do not forget to stop your instances after configuring the options.

Similarly, the remaining examples can be tested by starting instances and examining the contents of the appropriate subdirectories of /sys/fs/cgroup/.

Limiting CPU

Limit CPU resources using one of the following strategies. The cpu section of the configuration file can limit memory with the following:


This corresponds to a ratio versus other cgroups with cpu shares. Usually the default value is 1024. That means if you want to allow to use 50% of a single CPU, you will set 512 as value.

    shares = 512

A cgroup can get more than its share of CPU if there are enough idle CPU cycles available in the system, due to the work conserving nature of the scheduler, so a contained process can consume all CPU cycles even with a ratio of 50%. The ratio is only applied when two or more processes conflicts with their needs of CPU cycles.


You can enforce hard limits on the CPU cycles a cgroup can consume, so contained processes can’t use more than the amount of CPU time set for the cgroup. quota allows you to configure the amount of CPU time that a cgroup can use per period. The default is 100ms (100000us). So if you want to limit amount of CPU time to 20ms during period of 100ms:

    period = 100000
    quota = 20000


You can also restrict access to specific CPUs and associated memory nodes by using cpus/mems fields:

    cpus = "0-1"
    mems = "0-1"

Where container has limited access to CPU 0 and CPU 1.


It’s important to set identical values for both cpus and mems.

Limiting IO

You can limit and monitor access to I/O for block devices. Use the [blockIO] section of the configuration file to do this like so:

    weight = 1000
    leafWeight = 1000

weight and leafWeight accept values between 10 and 1000.

weight is the default weight of the group on all the devices until and unless overridden by a per device rule.

leafWeight relates to weight for the purpose of deciding how heavily to weigh tasks in the given cgroup while competing with the cgroup’s child cgroups.

To override weight/leafWeight for /dev/loop0 and /dev/loop1 block devices you would do something like this:

        major = 7
        minor = 0
        weight = 100
        leafWeight = 50
        major = 7
        minor = 1
        weight = 100
        leafWeight = 50

You could limit the IO read/write rate to 16MB per second for the /dev/loop0 block device with the following configuration. The rate is specified in bytes per second.

        major = 7
        minor = 0
        rate = 16777216
        major = 7
        minor = 0
        rate = 16777216


The execution control list is defined here. You can authorize the containers by validating both the location of the SIF file in the file system and by checking against a list of signing entities.

  tagname = "group2"
  mode = "whitelist"
  dirpath = "/tmp/containers"
  keyfp = ["7064B1D6EFF01B1262FED3F03581D99FE87EAFD1"]

Only the containers running from and signed with above-mentioned path and keys will be authorized to run.

Three possible list modes you can choose from:

Whitestrict: The SIF must be signed by ALL of the keys mentioned.

Whitelist: As long as the SIF is signed by one or more of the keys, the container is allowed to run.

Blacklist: Only the containers whose keys are not mentioned in the group are allowed to run.


When a container includes a GPU enabled application and libraries, Singularity (with the --nv option) can properly inject the required Nvidia GPU driver libraries into the container, to match the host’s kernel. This config file is the place where it searches for NVIDIA libraries in your host system. However, nvliblist.conf will be ignored in case of having nvidia-container-cli installed, which will be used to locate any nvidia libraries and binaries on the host system.

For GPU and CUDA support –nv option works like:

$ singularity exec --nv ubuntu.sif gpu_program.exec
$ singularity run --nv docker://tensorflow/tensorflow:gpu_latest

You can also mention libraries/binaries and they will be mounted into the container when the --nv option is passed.


Singularity provides full support for granting and revoking Linux capabilities on a user or group basis. By default, all Linux capabilities are dropped when a user enters the container system. When you decide to add/revoke some capabilities, you can do so using the Singularity capability options: Add, Drop and List.

For example, if you do:

$ sudo singularity capability add --user david CAP_SYS_RAWIO

You’ve let the user David to perform I/O port operations, perform a range of device-specific operations on other devices etc. To perform the same for a group of users do:

$ sudo singularity capability add --group mygroup audit_write

Use drop in the same format for revoking their capabilities.

To see a list of all users and their capabilities, simply do:

$ sudo singularity capability list --all

capability.json is the file maintained by Singularity where the capability commands create/delete entries accordingly.

To know more about the capabilities you can add do:

$ singularity capability add --help


The above commands can only be issued by root user(admin).

The –add-caps and related options will let the user request the capability when executing a container.


Secure Computing (seccomp) Mode is a feature of the Linux kernel that allows an administrator to filter system calls being made from a container. Profiles made up of allowed and restricted calls can be passed to different containers. Seccomp provides more control than capabilities alone, giving a smaller attack surface for an attacker to work from within a container.

You can set the default action with defaultAction for a non-listed system call. Example: SCMP_ACT_ALLOW filter will allow all the system calls if it matches the filter rule and you can set it to SCMP_ACT_ERRNO which will have the thread receive a return value of errno if it calls a system call that matches the filter rule. The file is formatted in a way that it can take a list of additional system calls for different architecture and Singularity will automatically take syscalls related to the current architecture where it’s been executed. The include/exclude-> caps section will include/exclude the listed system calls if the user has the associated capability.

Use the --security option to invoke the container like:

$ sudo singularity shell --security seccomp:/home/david/my.json my_container.sif

For more insight into security options, network options, cgroups, capabilities, etc, please check the Userdocs and it’s Appendix.