/usr/sbin/append-cmdline-arg is in initramfs-tools-ubuntu-touch 0.72.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | #!/bin/sh
BOOT="LNX boot KERNEL"
for i in $BOOT; do
path=$(find /dev -name "$i"|grep disk| head -1)
[ -n "$path" ] && break
done
OLDCMDLINE="$(abootimg -i $path|grep cmdline|sed -e 's/^.*cmdline = //') "
echo $OLDCMDLINE| grep -q "empty cmdline" && OLDCMDLINE=""
NEWCMDLINE="${OLDCMDLINE}${1}"
abootimg -u $path -c "cmdline=$NEWCMDLINE"
abootimg -i $path
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