macOS Catalina 10.15.x auto_master resets after upgrade

After upgrading to macOS Catalina 10.15, or installing a subsequent 10.15.x update, the auto_master file will be overwritten. You may need to re-append any custom lines to auto_master after the upgrade to restore your previously-working automounts.

Post-upgrade (or update), check the automount master mapping file (/etc/auto_master) to verify that your previously-working lines were removed.

sudo nano /etc/auto_master

The default contents probably look something like this:

#
# Automounter master map
#
+auto_master            # Use directory service
#/net                   -hosts          -nobrowse,hidefromfinder,nosuid
/home                   auto_home       -nobrowse,hidefromfinder
/Network/Servers        -fstab
/-                      -static

Optionally, save a backup copy of this original for future reference:

cd /etc
sudo cp auto_master auto_master.original

Now, append any lines you previously used to reference your other auto_* files. In my case, I have only one file named auto_nas.

/-                      auto_nas

Save your changes and then run the automount command to flush the cache and reload /etc/auto_master:

sudo automount -vc

Look for confirmation that each share mounted successfully:

automount: /System/Volumes/Data/Users/me/Nas/media mounted
automount: /System/Volumes/Data/Users/me/Nas/storage mounted
automount: /System/Volumes/Data/Users/me/Nas/archives mounted

If you happen to be mounting any shares into your user directory, make sure you have updated your mountpoints to match Catalina’s new directory structure. Otherwise, automount will complain about /Users/you/mountpoint not existing.

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