How to run commands in an instance

LXD allows to run commands inside an instance using the LXD client, without needing to access the instance through the network.

For containers, this always works and is handled directly by LXD. For virtual machines, the lxd-agent process must be running inside of the virtual machine for this to work.

To run commands inside your instance, use the lxc exec command. By running a shell command (for example, /bin/bash), you can get shell access to your instance.

Run commands inside your instance

To run a single command from the terminal of the host machine, use the lxc exec command:

lxc exec <instance_name> -- <command>

For example, enter the following command to update the package list on your container:

lxc exec my-instance -- apt-get update

Execution mode

LXD can execute commands either interactively or non-interactively.

In interactive mode, a pseudo-terminal device (PTS) is used to handle input (stdin) and output (stdout, stderr). This mode is automatically selected by the CLI if connected to a terminal emulator (and not run from a script). To force interactive mode, add either --force-interactive or --mode interactive to the command.

In non-interactive mode, pipes are allocated instead (one for each of stdin, stdout and stderr). This method allows running a command and properly getting separate stdin, stdout and stderr as required by many scripts. To force non-interactive mode, add either --force-noninteractive or --mode non-interactive to the command.

User, groups and working directory

LXD has a policy not to read data from within the instances or trust anything that can be found in the instance. Therefore, LXD does not parse files like /etc/passwd, /etc/group or /etc/nsswitch.conf to handle user and group resolution.

As a result, LXD doesn’t know the home directory for the user or the supplementary groups the user is in.

By default, LXD runs commands as root (UID 0) with the default group (GID 0) and the working directory set to /root. You can override the user, group and working directory by specifying absolute values.

You can override the default settings by adding the following flags to the lxc exec command:

  • --user - the user ID for running the command

  • --group - the group ID for running the command

  • --cwd - the directory in which the command should run

Environment

You can pass environment variables to an exec session in the following two ways:

Set environment variables as instance options

To set the <ENVVAR> environment variable to <value> in the instance, set the environment.<ENVVAR> instance option (see environment.*):

lxc config set <instance_name> environment.<ENVVAR>=<value>
Pass environment variables to the exec command

To pass an environment variable to the exec command, use the --env flag. For example:

lxc exec <instance_name> --env <ENVVAR>=<value> -- <command>

In addition, LXD sets the following default values (unless they are passed in one of the ways described above):

Variable name

Condition

Value

PATH

-

Concatenation of:

  • /usr/local/sbin

  • /usr/local/bin

  • /usr/sbin

  • /usr/bin

  • /sbin

  • /bin

  • /snap (if applicable)

  • /etc/NIXOS (if applicable)

LANG

-

C.UTF-8

HOME

running as root (UID 0)

/root

USER

running as root (UID 0)

root

Get shell access to your instance

If you want to run commands directly in your instance, run a shell command inside it. For example, enter the following command (assuming that the /bin/bash command exists in your instance):

lxc exec <instance_name> -- /bin/bash

By default, you are logged in as the root user. If you want to log in as a different user, enter the following command:

lxc exec <instance_name> -- su --login <user_name>

To exit the instance shell, enter exit or press Ctrl+d.

Note

Depending on the operating system that you run in your instance, you might need to create a user first.