How can I work out what program is keeping a disk open?
Use sudo lsof and grep for the name of the disk you’re trying to eject.
Sometimes when I go to eject a disk on macOS, I can’t and the computer won’t tell me why:
I’ve wrecked an APFS volume by force ejecting it so I’d rather avoid that if I can, but how do I know what programs are using it? Sometimes it tells me the name of macOS apps but other times it just knows that something is using the disk.
Based on a few Internet searches, I’ve cobbled together the following steps.
First, use lsof to see all open files, and grep for the name of the volume I’m trying to eject:
$ sudo lsof | grep Saffron
bztransmi 60758 root 6r REG 1,27 4163181904 808769 /Volumes/Media (Saffron)/plex/Movies/Still Alice.mp4
mds 98474 root 6r DIR 1,27 992 2 /Volumes/Media (Saffron)
mds 98474 root 34r DIR 1,27 14272 21 /Volumes/Media (Saffron)/.Spotlight-V100/Store-V2/A448E67A-FA2B-45BC-B6D9-9EF563D5719E
mds 98474 root 56r DIR 1,27 992 2 /Volumes/Media (Saffron)
mds 98474 root 73w REG 1,27 49 1270183 /Volumes/Media (Saffron)/.Spotlight-V100/Store-V2/A448E67A-FA2B-45BC-B6D9-9EF563D5719E/journals.scan/journal.6898
mds_store 98476 root twd DIR 1,27 14272 21 /Volumes/Media (Saffron)/.Spotlight-V100/Store-V2/A448E67A-FA2B-45BC-B6D9-9EF563D5719E
… skip several hundred entries …
mds_store 98476 root 362u REG 1,27 4096 1058890 /Volumes/Media (Saffron)/.Spotlight-V100/Store-V2/A448E67A-FA2B-45BC-B6D9-9EF563D5719E/live.12.indexHead
If it’s a user-visible app, I can stop it the “proper” way. For example, bztransmit is part of Backblaze – it was trying to upload a file from the disk, so I used the Backblaze menubar helper to pause the current backup. Now Backblaze is no longer holding the disk open!
If it’s mds_store, I just kill it by ID. This is the Spotlight indexer and I don’t know of a “good” way to interrupt it – but I’ve also never seen any issues from stopping it using kill. I can get the process ID from the lsof output.
$ sudo kill -9 98476