thin-edge.io installation with deb files need getent

[bjoernsauer]

Describe the bug
The installation of thin-edge.io with the Debian Packages need getent. This command is not available on busybox.

To Reproduce
Try to install tedge.deb on a target that runs with busybox.

Expected behavior
Avoid getent use grep for example to check if a group or user exists.

Environment (please complete the following information):

• OS
  Custom Yocto Linux
• Hardware [incl. revision]
  Phoenix Contact Controller AXC F 2152
• System-Architecture [e.g. result of "uname -a"]
  Linux axcf2152 5.4.257-rt87-pxc SMP PREEMPT_RT Thu Nov 16 06:49:45 UTC 2023 armv7l armv7l armv7l GNU/Linux
• thin-edge.io version
  v1.1.1

Additional context

root@axcf2152# dpkg -i -D=2 /opt/plcnext/apps/60002172000584/images/tedge/arm/tedge.deb 
(Reading database ... 32 files and directories currently installed.)
Preparing to unpack .../images/tedge/arm/tedge.deb ...
/var/lib/dpkg/tmp.ci/preinst: line 9: getent: command not found
groupadd: group 'tedge' already exists
dpkg: error processing archive /opt/plcnext/apps/60002172000584/images/tedge/arm/tedge.deb (--install):
 new tedge:armhf package pre-installation script subprocess returned error exit status 9
Errors were encountered while processing:
 /opt/plcnext/apps/60002172000584/images/tedge/arm/tedge.deb

[reubenmiller]

We would have to avoid doing a manual grep on /etc/passwd and /etc/group as this doesn't work if the OS uses custom user/groups controlled by NSS, namely Fedora IoT does not store the values under aforementioned files during installation due to its usage of rpm-ostree (to enable rolling back of packages etc.).

@bjoernsauer I think thin-edge.io can switch to use checks with id (for both user and group), and this should work in busybox as id is included in the busy-box list of commands

[bjoernsauer]

Hi @reubenmiller, yes id would be available. Maybe check for getent and prefere to use it if it is available and fall back to a alternative implementation with id or something else.

[reubenmiller]

We'll see what makes more sense, we generally want to try to avoid too many different ways of doing things as it makes the script a bit more difficult to read and maintain, however only if we can be 100% sure that using id "works everywhere"

Below are the proposed commands to use to check if existence of the tedge user and group:

# Check if user 
if ! id -u tedge >/dev/null 2>&1; then
  echo "tedge user does not exist"
fi

# Check if group exists
if ! id -g tedge >/dev/null 2>&1; then
  echo "tedge group does not exist"
fi

[reubenmiller]

Though I guess we could do some simple wrapper functions which have some fallback logic to ensure maximum compatibility:

group_exists() {
    name="$1"
    if command_exists id; then
        id -g "$name" >/dev/null 2>&1
    elif command_exists getent; then
        getent group "$name" >/dev/null 2>&1
    else
        # Fallback to plain grep, as busybox does not have getent
        grep -q "^${name}:" /etc/group
    fi
}

user_exists() {
    name="$1"
    if command_exists id; then
        id -u "$name" >/dev/null 2>&1
    elif command_exists getent; then
        getent passwd "$name" >/dev/null 2>&1
    else
        # Fallback to plain grep, as busybox does not have getent
        grep -q "^${name}:" /etc/passwd
    fi
}

[bjoernsauer]

I can confirm that the proposed solution works for my target system.

[reubenmiller]

There is already a PR in the works, #2942

[reubenmiller]

@bjoernsauer The feature is already merged, so you can try out the published packages from the tedge-main channel from cloudsmith.io.

Or if you're using the install convenience script, you can use an argument to use the main channel:

wget -O thin-edge.io/install.sh | sh -s -- --channel main