I've just started using a new MacBook Pro, which has Mac OS X 10.10.1 "Yosemite" pre-installed. I was surprised to find paths like /Volumes/Untitled in my /Volumes directory.
% ls -ld /Volumes/Untit*
d--x--x--x+ 3 root admin 102 17 Dec 17:10 /Volumes/Untitled
d--x--x--x+ 3 root admin 102 18 Dec 12:34 /Volumes/Untitled 1
d--x--x--x+ 3 root admin 102 19 Dec 11:44 /Volumes/Untitled 2
d--x--x--x+ 3 root admin 102 20 Dec 11:45 /Volumes/Untitled 3
d--x--x--x+ 3 root admin 102 22 Dec 07:17 /Volumes/Untitled 4
d--x--x--x+ 3 root admin 102 25 Dec 22:23 /Volumes/Untitled 5
d--x--x--x+ 3 root admin 102 26 Dec 10:41 /Volumes/Untitled 6
Each directory appears to be empty, except for an empty .Trashes subdirectory:
% sudo ls -lR /Volumes/Untitled
total 0
d-wx-wx-wt@ 2 root admin 68 17 Dec 17:08 .Trashes
/Volumes/Untitled/.Trashes:
I am familiar with entries in /Volumes/* being paths to external storage volumes. I have an external solid-state drive (SSD) mounted, and it has its own named /Volumes/mySSD entry. I have a couple of drives mounted from a file server, and they have their own named /Volumes/serverA etc. entries. In previous Macs and previous Mac OS X versions, I didn't see entries like /Volumes/Untitled.
The timestamps on the Untitled* directories are interesting. The first one is from about when I unpacked the new MacBook Pro for the first time. The most recent one is from about when I started up the computer this morning. If I notice changes in the days ahead, I'll update this question.
I do not see other answers on AskDifferent explaining entries like these. There are answers like Problems creating Yosemite USB bootable drive which mention paths like /Volumes/Untitled 2, but those appear to be paths for actual mounted disk devices that happen to have no volume label. I also have a query in to Apple Support. If they tell me something useful, I'll post it as an answer.
Update 1: A few answers to questions, and further details that seem relevant:
Q: Can you run mount to see whether/which of these mount points actually point to an existing drive? A: I did so, and got this:
% mount
/dev/disk1 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
localhost:/TdCrZmzerGhdW5I605Hbd7 on /Volumes/MobileBackups (mtmfs, nosuid, read-only, nobrowse)
//userme@Gemini%28AFP%29._afpovertcp._tcp.local/Qmultimedia on /Volumes/Qmultimedia (afpfs, nodev, nosuid, mounted by userme)
//userme@Gemini%28AFP%29._afpovertcp._tcp.local/serverA on /Volumes/serverA (afpfs, nodev, nosuid, mounted by userme)
/dev/disk2s1 on /Volumes/mySSD (hfs, local, nodev, nosuid, journaled)
Q: Do you have a camera card in the slot, or other computers/devices on the network sharing their content? A: No camera card. Yes, other devices, as noted above: an external SSD, and a couple of drives mounted from a file server.
Also relevant: the external SSD drive has two partitions. One is HFS+ formatted, and is labelled "mySSD" [exact name changed to preserve privacy]. The other partition is ext2 formatted by a Linux system, and as far as I can tell it has no volume label. It's visible from Disk Utility, but doesn't mount as a Mac volume. The drive is connected by USB to the MacBook Pro.
Also relevant: I used Migration Assistant to bring my environment from a Time Machine backup of an older Mac to this computer. I migrated users, applications, system settings, and other files. Among the software installed on the old computer was fuse-ext2 0.0.7, a utility to let Mac OS computers mount ext2 partitions. This software was running on the new computer:
% fuse-ext2 --version
[...snip...]
fuse-ext2 0.0.7 27 - FUSE EXT2FS Driver
Copyright (C) 2008-2009 Alper Akcan <alper.akcan@gmail.com>
Copyright (C) 2009 Renzo Davoli <renzo@cs.unibo.it>
[...snip...]
I also discovered that every time I plugged the external drive into the USB port while the MacBook Pro was running, or every time the computer restarted with the external drive plugged in, a new /Volumes/Untitled* entry appeared.
Finally, I found that fuse-ext2 was writing a log file at /private/var/log/fuse-ext2_util.log. Below are excerpts of the contents. I added line wraps in long lines. Note in particular the time stamps and the path name parameters:
2014-12-17 17:06:36: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/Contents/Resources/../
../fuse-ext2.util" "-p" "disk2s2" "removable" "readonly" "" "" "" "" ""
.... [snip] ....
2014-12-17 17:08:24: [Mount] Entering function Mount...
2014-12-17 17:08:24: [Mount] Processing argument "/dev/disk2s2"
2014-12-17 17:08:24: [Mount] Processing argument "/Volumes/Untitled"
2014-12-17 17:08:24: [Mount] Got plain device "/dev/disk2s2"
2014-12-17 17:08:24: [Mount] Got raw device "/dev/rdisk2s2"
2014-12-17 17:08:24: [Mount] Invoking:
2014-12-17 17:08:24: [Mount] "/usr/local/bin/fuse-ext2.wait" "/Volumes/Untitled"
"5" "/usr/local/bin/fuse-ext2" "/dev/disk2s2" "/Volumes/Untitled"
"-oauto_xattr,defer_permissions,local"
2014-12-17 17:08:30: [Mount] /usr/local/bin/fuse-ext2.wait returned with retval: 0
2014-12-17 17:08:30: [Mount] Output from mount operation: Mounting /dev/disk2s2
Read-Only.
Use 'force' or 'rw+' options to enable Read-Write mode
/Library/Filesystems/http://fusefs.fs/Support/fusefs.kext failed to load
- (libkern/kext) link error; check the system/kernel logs for errors or
try kextutil(8).
the MacFUSE file system is not available (71)
fuse-ext2: version:'0.0.7', fuse_version:'27' [main
(../../fuse-ext2/fuse-ext2.c:324)]
fuse-ext2: enter [do_probe (../../fuse-ext2/do_probe.c:30)]
fuse-ext2: leave [do_probe (../../fuse-ext2/do_probe.c:55)]
fuse-ext2: opts.device: /dev/disk2s2 [main (../../fuse-ext2/fuse-ext2.c:351)]
fuse-ext2: opts.mnt_point: /Volumes/Untitled [main
(../../fuse-ext2/fuse-ext2.c:352)]
fuse-ext2: opts.volname: [main (../../fuse-ext2/fuse-ext2.c:353)]
fuse-ext2: opts.options: auto_xattr,defer_permissions,local [main
(../../fuse-ext2/fuse-ext2.c:354)]
fuse-ext2: parsed_options: auto_xattr,defer_permissions,local,allow_other,local,
noappledouble,ro,fsname=/dev/disk2s2,fstypename=ext2,volname=disk2s2 [main
(../../fuse-ext2/fuse-ext2.c:355)]
fuse-ext2: mounting read-only [main (../../fuse-ext2/fuse-ext2.c:371)]
Did not receive a signal within 5.000000 seconds. Exiting...
2014-12-17 17:08:30: [Mount] Executing "/usr/local/bin/fuse-ext2.daemon"
2014-12-17 17:08:30: [Mount] Exiting function mount...
2014-12-18 12:24:40: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/Contents/Resources/../
../fuse-ext2.util" "-p" "disk3s2" "removable" "readonly" "" "" "" "" ""
.... [snip] ....
2014-12-19 01:45:10: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/fuse-ext2.util" "-m" "-o" "nodev"
"-o" "noowners" "-o" "nosuid" "/dev/disk2s2" "/Volumes/Untitled 2"
.... [snip] ....
2014-12-19 01:45:15: [Mount] Exiting function mount...
2014-12-20 10:56:44: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/Contents/Resources/../
../fuse-ext2.util" "-p" "disk2s2" "removable" "readonly" "" "" "" "" ""
.... [snip] ....
2014-12-20 10:56:45: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/fuse-ext2.util" "-m" "-o" "nodev"
"-o" "noowners" "-o" "nosuid" "/dev/disk2s2" "/Volumes/Untitled 3"
.... [snip] ....
.... [snip] ....
2014-12-26 13:25:57: [Mount] Exiting function mount...
2014-12-26 13:41:32: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/Contents/Resources/../
../fuse-ext2.util" "-p" "disk2s2" "removable" "readonly" "" "" "" "" ""
.... [snip] ....
2014-12-26 13:41:32: fuse-ext2 script invoked with command line
"/System/Library/Filesystems/http://fuse-ext2.fs/fuse-ext2.util" "-m" "-o" "nodev"
"-o" "noowners" "-o" "nosuid" "/dev/disk2s2" "/Volumes/Untitled 8"
.... [snip] ....
2014-12-26 13:41:38: [Mount] Exiting function mount...
This information was enough to give me a diagnosis, and I'm supplying that as an answer below. I included a lot of detail in the update so that search engines will index the clues, for future people with this problem.
But if I tried to look around in the Terminal to potentially delete these, it only found the reasonable ones:
