systemd-debug-generator — Generator for enabling a runtime debug shell and masking specific units at boot
/usr/lib/systemd/system-generators/systemd-debug-generator
systemd-debug-generator is a generator that provides some debugging functionality.
systemd-debug-generator implements systemd.generator(7).
systemd-debug-generator understands the following kernel command line parameters:
systemd.mask=, rd.systemd.mask=¶These options take a unit name as argument. The unit specified is masked for the
runtime (i.e. for this session — from boot to shutdown), similarly to the effect of
systemctl(1)'s
mask command. This is useful to boot with certain units removed from the initial
boot transaction for debugging system startup. May be specified more than once. The option prefixed
with "rd." is honored only in the initrd, while the one without prefix is only
honored on the host.
systemd.wants=, rd.systemd.wants=¶These options take a unit name as argument. A start job for this unit is added to the
initial transaction. This is useful to start one or more additional units at boot. May be specified
more than once. The option prefixed with "rd." is honored only in the initrd, while
the one that is not prefixed only on the host.
systemd.debug_shell, rd.systemd.debug_shell, systemd.default_debug_tty=, rd.systemd.default_debug_tty=¶If the systemd.debug_shell or
rd.systemd.debug_shell option is specified, the debug shell service
"debug-shell.service" is pulled into the boot transaction and a debug shell will be
spawned during early boot. By default, /dev/tty9 is used, but a specific tty
can also be specified, either with or without the /dev/ prefix. To set the tty
to use without enabling the debug shell, the systemd.default_debug_tty= option can
be used which also takes a tty with or without the /dev/ prefix. Note that the
shell may also be turned on persistently by enabling it with
systemctl(1)'s
enable command. The options prefixed with "rd." are honored only
in the initrd, while the ones without prefix are only honored on the host.
systemd.break=, rd.systemd.break=¶Takes one of pre-udev, pre-basic,
pre-mount, or pre-switch-root (the default for the
"rd." option). It also accepts multiple values separated by comma
(","). These options allow to pause the boot process at a certain point and spawn a
debug shell. After exiting this shell, the system will resume booting. The option prefixed with
"rd." is honored only in the initrd, while the one without prefix is only honored on
the host.
Table 1. Available breakpoints
| Breakpoints | Description | Can be used in the initrd | Can be used on the host |
|---|---|---|---|
pre-udev | Before starting to process kernel uevents, i.e., before systemd-udevd.service starts. | ✓ | ✓ |
pre-basic | Before leaving early boot and regular services start, i.e., before basic.target is reached. | ✓ | ✓ |
pre-mount | Before the root filesystem is mounted, i.e., before sysroot.mount starts. | ✓ | ✗ |
pre-switch-root | Before switching from the initrd to the real root. | ✓ | ✗ |
systemd.extra-unit.*¶Credentials prefixed with "systemd.extra-unit." specify additional
units to add to the final system. Note that these additional units are added to both the initrd and
the final system. ConditionPathExists=!/etc/initrd-release can be used to make
sure the unit is conditioned out in the initrd. Note that this can also be used to mask units, by
simply specifying an empty value.
systemd.unit-dropin.*¶Credentials prefixed with "systemd.unit-dropin." add drop-ins for
the corresponding units in the final system. Each credential must be suffixed with the full unit name
including the unit extension. Its contents must be a valid unit drop-in file. Optionally, the unit
name may be followed with "~", followed by the drop-in name without the
".conf" suffix. If not specified, the name of the generated drop-in will be
"50-credential.conf". Note that these additional drop-ins are added to both the
initrd and the final system.