Reinventing Linux home directories with systemd-homed

Managing Users

Like other systemd services, systemd-homed comes with its own command-line management utility. You will not be able to use the useradd utility or other classic command-line tools to manage systemd-homed users. Instead, use the homectl command to create, remove, or change a user directory. The homectl command supports several subcommands and options for setting up a user or changing user account settings.

For example, to create the user bennie for someone whose real name is Bennie Beanbag and to assign 400MB of disk space to the user directory, use:

homectl create bennie --real-name="Bennie Beanbag" --disk-size=400M

See the box entitled "More on homectl" for some of the basic homectl commands, or look for the homectl documentation to study the many options and command variants [3].

More on homectl

The homectl command has the following syntax:

homectl [OPTIONS...] {SUBCOMMAND} [NAME...]

The numerous options include format settings, user record properties, encryption settings, and more [3]. Some of the important subcommands are:

  • list – list all home directories currently managed by the service
  • activate – activate one or more home directories
  • create – create a new home directory with the specified name
  • passwd – change the password on the specified home directory and user account
  • resize – change the setting for the amount of disk space assigned to the specified home directory
  • lock – temporarily suspend access to the user's home directory and remove any associated crypto keys from memory

The wide range of options and subcommands within a single command is similar to the format used with other systemd services. Unlike old-school command-line utilities, which tended to have a single, specific purpose, the broad and versatile systemd utilities encapsulate several different tasks within a single command structure, which leads to very tidy and hierarchical documentation. However, like systemd itself, it poses a challenge to those who prefer simple tools with a single purpose.

What's It All For?

The systemd developers do not think of systemd-homed as a solution for all situations. First of all, this technique is not intended for system users (users with a UID<1000). In general, systemd-homed is intended for end-user accounts. The ability to move a complete self-contained user home directory – not just user files – but the complete configuration and even login information, could be a major benefit in some environments. But even if you don't plan on migrating your home directory, having a user directory system that is integrated with the rest of systemd will be a welcome development for many users and admins. Of course, the chorus of users who don't like systemd in the first place are certainly not going to like it more because of systemd-homed.

Several potential users have already expressed concerns with how systemd-homed will handle SSH. If you've been paying close attention, you've probably already come to realize that, if systemd-homed leaves the user's home directory encrypted until successful login authentication, how will users be able to log into a remote machine via SSH? Remember, the .ssh directory exists within the user's home directory (in ~/.ssh/).

No universal solution to the SSH problem exists at this point, but, as Lennart Poettering recently pointed out on Reddit, systemd-homed is intended for laptops, workstations, and client systems "…machines you SSH from a lot more than SSH to…" [4]. The primary purpose is to support local login on end-user systems.

The biggest fear that comes with systemd-homed is that users and administrators will have to learn a new way of handling authentication and home directories. This is especially true for app developers, who might very well have to make serious changes to how their applications deal with these issues.

And although change is something most feared, others believe this change might well be a change for the better. Linux has been in need of improvement with how it handles user authentication and the home directory. For those who have been hoping for better home encryption, a centralized authentication system, and more portable home directories, systemd-homed is exactly what you've been looking for.

You can test systemd-homed in v245-rc1 from GitHub [5]. The installation of this system is not for the faint of heart, so it's best to wait until the official release is available to kick the tires. The release of systemd 245 should happen sometime this year (2020).

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