reboot by kexec

kexec-reboot.py

#!/usr/bin/env python3

from argparse import ArgumentParser
from contextlib import suppress
import json
import os
import re
import shlex
import shutil
import subprocess as sp
import sys

def kexec_main(a):
    unshare_env = f'reboot_unshared_{os.getpid()}'
    if unshare_env not in os.environ:
        os.environ[unshare_env] = '1'
        c = ['unshare', '-m', sys.executable] + sys.argv
        os.execvp(c[0], c)

    entry = None
    for e in json.loads(sp.run(['bootctl', '--json=short', 'list'], check=True, stdout=sp.PIPE).stdout):
        if a.boot_entry is not None:
            if e['id'] == a.boot_entry:
                entry = e
                break
        else:
            if e['isDefault']:
                entry = e
                break

    if entry is None or 'version' not in entry:
        raise RuntimeError('no suitable boot entry found')

    version = entry['version']
    kernel = os.path.join(entry['root'], entry['linux'].lstrip('/'))
    option = entry.get('options', '') + ' rd.shell=0 rd.break=0 rd.timeout=300 rd.emergency=reboot'
    print(f'Selected kernel {kernel} version {version}')

    dracutcmd = ['dracut', '--no-compress']
    if 'rd.luks.uuid' in option and os.path.exists('/etc/crypttab'):
        luksuuid = []
        for o in option.split():
            if o.startswith('rd.luks.uuid='):
                u = o.split('=', 1)[1]
                if u.startswith('keysource:'):
                    u = u.split(':', 1)[1]
                if u.startswith('luks-'):
                    u = u[5:]
                luksuuid.append(u)
        keyfiles = set()
        with open('/etc/crypttab') as f:
            for l in f:
                l = l.split()
                if len(l) >= 3 and l[1].startswith('UUID=') and l[2].startswith('/'):
                    uuid = l[1][5:]
                    for u in luksuuid:
                        if uuid.startswith(u):
                            keyfiles.add(l[2])
        if keyfiles:
            dracutcmd += ['--install', '/etc/crypttab']
            for f in keyfiles:
                dracutcmd += ['--install', f]

    dracutcmd += ['/tmp/initrd.img', version]
    sp.run(['mount', '-t', 'tmpfs', 'none', '/tmp'], stdin=sp.DEVNULL, check=True)
    sp.run(dracutcmd, stdin=sp.DEVNULL, check=True)

    sp.run(['kexec', '-l', '-a', '--append=' + option, '--initrd=/tmp/initrd.img', kernel], stdin=sp.DEVNULL, check=True)

    if not a.load:
        sp.run(['systemctl', '--no-block', 'kexec'], stdin=sp.DEVNULL, check=True)

def main():
    a = ArgumentParser(description='reboot by kexec')
    a.add_argument('--load', '-l', action='store_true', help='load kernel but do not reboot')
    a.add_argument('boot_entry', nargs='?', help='select boot entry')

    kexec_main(a.parse_args())

if __name__ == '__main__':
    main()

kexec-reboot.service.in

[Unit]
DefaultDependencies=no
Wants=kexec.target
Before=kexec.target

[Service]
Type=oneshot
ExecStart=@libexec@/kexec-reboot.py --load

kexec-reboot.target

[Unit]
DefaultDependencies=no
Wants=kexec-reboot.service
AllowIsolate=yes

[Install]
Alias=reboot.target
Alias=ctrl-alt-del.target

PKGBUILD

pkgname=kexec-reboot
pkgver=0.20230916.0
pkgrel=1
pkgdesc='reboot by kexec'
arch=(any)
license=(Unlicense)

depends=(
	systemd
	python
	util-linux
	kexec-tools
)
makedepends=(
	sed
)

source=(
	kexec-reboot.py
	kexec-reboot.service.in
	kexec-reboot.target
)
cksums=(
	SKIP
	SKIP
	SKIP
)

build() {
	sed 's!@libexec@!/usr/lib!' < "$srcdir/kexec-reboot.service.in" > "$srcdir/kexec-reboot.service"
}

package() {
	install -Dm644 -t "$pkgdir/usr/lib/systemd/system" "$srcdir/kexec-reboot.service"
	install -Dm644 -t "$pkgdir/usr/lib/systemd/system" "$srcdir/kexec-reboot.target"
	install -Dm755 -t "$pkgdir/usr/lib" "$srcdir/kexec-reboot.py"
}