nix-uninstall.sh

#!/bin/bash
# 
# Purpose: simple script to remove nix from MacOS
# author: Jason Schechner, nixfan@jasons.us
# Last updated: 2022-05-12
#
# conventions used here:
# * capitalized variables don't change during script run
# * exit codes: 0=success, 1=minor problem, 2=major problem 
#
# to do
# * ?
# 
# changelog
# * 2022-05-12 - initial creation

# set variables. You can override these by exporting the same variable in your shell before running me.
#FAILSAFE="echo" # uncomment this to neuter the script so it runs checks but doesn't do anything.
NIX_RM_LOGFILE=${NIX_RM_LOGFILE:-$(basename $0).log}
LAUNCH_DAEMONS="org.nixos.darwin-store org.nixos.nix-daemon"
LAUNCH_DAEMON_HOME=/Library/LaunchDaemons

# you shouldn't have to touch anything below this line
chatter(){
# always log output, and echo to the user if in VERBOSE mode 
    echo "$1" >> ${NIX_RM_LOGFILE}
    test "${VERBOSE}" && echo "$1"
}

printhelp(){
cat <<EOB
Simple script to remove nix from MacOS
Usage: $(basename $0) [-f|-h|-v]
 -f|--force    = run without initial confirmation check. BE CAREFUL!
 -h|--help     = help (you're looking at it!)
 -v|--verbose  = verbose mode
EOB
exit 0
}

pfc(){
# pre-flight check
# verify writable log file
test -w ${NIX_RM_LOGFILE} || touch ${NIX_RM_LOGFILE} || { echo "Unable to create log file, ${NIX_RM_LOGFILE}. Exiting."; exit 2; }
DATESTAMP=$(date +%Y%m%d.%H%M)
echo "${DATESTAMP} - Starting nix removal run. Logging to ${NIX_RM_LOGFILE}." | tee -a ${NIX_RM_LOGFILE}
# clear variables
unset backupdotfile dotfile gonogo launchdaemon nixusers usernumber FORCE VERBOSE
exitcode=0
case "$1" in
    "") 
    ;;
    -f|--force)
        FORCE=1
    ;;
    -v|--verbose)   
        echo "verbose mode"
        VERBOSE=1
    ;;
    -h|--help)        
        printhelp
    ;;
    *) 
        echo "unknown argument: $1. Perhaps you need help..."
    printhelp
esac

if test -z "${FORCE}" -a -z "${FAILSAFE}"; then
    echo "Run in active mode? This could make irreversible changes to your computer."
    read -n 1 -p "'Y' to continue. Anything else to run in safe mode which makes no changes... " gonogo
    if test "${gonogo}" == "y" -o "${gonogo}" == "Y"; then
        chatter "Active mode. Possibly making changes." 
    else
        FAILSAFE="echo"
    fi
    echo
fi
test "${FAILSAFE}" == "echo" && echo "Failsafe mode." | tee -a ${NIX_RM_LOGFILE}
}

# main
pfc "$1"

# check if launch daemons are loaded and, if so, unload them. Then delete pfiles
for launchdaemon in ${LAUNCH_DAEMONS}; do 
    if test -f ${LAUNCH_DAEMON_HOME}/${launchdaemon}.plist; then
    chatter "killing and removing launch daemon ${launchdaemon}"
    if launchdaemon list ${launchdaemon} > /dev/null 2>&1; then
        ${FAILSAFE} sudo launchctl kill ${launchdaemon}
    fi
        ${FAILSAFE} sudo launchctl unload ${LAUNCH_DAEMON_HOME}/${launchdaemon}.plist || exitcode=1
    ${FAILSAFE} sudo rm ${LAUNCH_DAEMON_HOME}/${launchdaemon}.plist || exitcode=2
    fi
done

# delete nix users
nixusers=$(dscl . list /Users | grep -c nixbld)
if test ${nixusers} -ge 1; then
    chatter "Deleting ${nixusers} nix users"
    for usernumber in $(seq 1 ${nixusers}); do 
    ${FAILSAFE} sudo dscl . delete /Users/_nixbld${usernumber} || { chatter "unable to remove user _nixbld${usernumber}"; exitcode=2; }
    # It looks like newer versions of Nix don't create directories for nixbld*, but in case you have them from an old rev...
    if test -d /Users/nixblkd${usernumber}; then
        ${FAILSAFE} sudo rm -rf /Users/nixbld${usernumber} || exitcode=1
    fi
    done
fi

# delete group
if dscl . -list /Groups | grep -q nixbld; then
    chatter "Deleting nixbld group"
    ${FAILSAFE} /usr/bin/dscl . -delete "/Groups/nixbld" || exitcode=1
fi

# restore dot files if any backups exist
if test $(ls /etc/*.backup-before-nix 2> /dev/null | wc -l) -ge 1; then
    for backupdotfile in /etc/*.backup-before-nix; do
    dotfile=${backupdotfile/.backup-before-nix}
    chatter "backing up nix-enabled dot file and restoring original: ${dotfile}"
    ${FAILSAFE} sudo mv ${dotfile} ${dotfile}.backup-before-removing-nix.${DATESTAMP} || exitcode=1
    ${FAILSAFE} sudo mv ${backupdotfile} ${dotfile} || exitcode=1
    done
fi

# make sure nix isn't in any of the relevant dot files
if grep -q 'nix' /etc/{profile,bashrc,bash.bashrc,zshrc}; then 
    echo "FAULT: nix is still present in at least one of your dot files. Fix this before reinstalling!"
    grep -l 'nix' /etc/{profile,bashrc,bash.bashrc,zshrc}
    exitcode=2
fi

for filesystemfile in fstab synthetic; do
    if grep -E -q '/?nix ' /etc/${filesystemfile} > /dev/null 2>&1 ; then
    echo "Updating filesystem file ${filesystemfile}"
    ${FAILSAFE} sudo sed -i.backup-before-removing-nix.${DATESTAMP}  '/\/nix/d' /etc/${filesystemfile} || exitcode=1
    fi
done

# delete apfs volume "Nix Store"
if diskutil list | grep -q "Nix Store"; then
    echo "deleting 'Nix Store' APFS volume"
    ${FAILSAFE} sudo diskutil apfs deleteVolume "Nix Store" || exitcode=1
fi

# wrap up
echo "$(date +%Y%m%d.%H%M) - Completed nix removal run." | tee -a ${NIX_RM_LOGFILE}
# enable verbose mode so that exit messages go to the user and log file
VERBOSE=1
case ${exitcode} in
    0) chatter "SUCCESS. Nix removal steps finished. Reboot to complete the process.";;
    1) chatter "SUCCESS - probably. Minor problem during nix removal steps. It's likely safe to proceed and reboot but check the log first.";;
    2) chatter "FAIL: Major failure during nix removal steps. Fix those before proceeding.";;
    *) chatter "UNKNOWN: unknown exitcode (${exitcode}). You should not see this. Strange things are afoot."
esac
echo >> ${NIX_RM_LOGFILE}
exit ${exitcode}