postinst is in usbmuxd 1.1.0-2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
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 16 | #!/bin/sh
set -e
# creating plugdev group if he isn't already there
if ! getent group plugdev >/dev/null; then
addgroup --system plugdev
fi
# creating usbmux user if he isn't already there
if ! getent passwd usbmux >/dev/null; then
adduser --system --ingroup plugdev \
--home /var/lib/usbmux --no-create-home \
--gecos "usbmux daemon" \
usbmux
fi
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