After reading various old posts here and elsewhere, I attempted to move my Linux Mint 12-based system's BOINC (6.12.33) client directory. I:

[*] Waited until all projects finished all their tasks.
[*] Created /home/boinc with boinc:boinc owner & group.
[*] Changed BOINC_DIR from /var/lib/boinc-client to /home/client in /etc/default/boinc-client. (Also changed it in /etc/init.d/boinc-client, though code looks like it's not necessary, as default overrides.)
[*] Moved everything from /var/lib/boinc-client to /home/boinc, including symlinks, and preserving owner & group settings.
[*] Created symlink /var/lib/boinc-client -> /home/boinc (just in case).
[*] Added <data_dir>/home/boinc</data_dir> to (otherwise empty) <options> section of cc_config.xml in /home/boinc.
[*] Did `sudo /etc/init.d/boinc-client restart` to restart BOINC.

BOINC manager no longer sees anything. All its settings appear to be installed-version defaults (no connection to cc_config.xml or global_prefs_override.xml settings). Telling it to "read config file" or "read local prefs file" changes nothing. It doesn't react to "attach project", either.

I've tried rebooting the system. I've even removed BOINC and reinstalled it via Synaptic; it preserved the changed file settings but the manager still failed to see anything.

(I haven't tried "complete remove" because it would defeat the purpose of changing default settings. Nor have I tried building BOINC from source, as I'd hope that the config files with data-directory settings exist so that one can simply configure, rather than rebuild, the software. Besides, executing `cd /usr/bin; strings boinc boinccmd boincmgr` doesn't reveal any inclusion of /var/lib/boinc-client in the binaries.

Tracing through the expected execution of /etc/init.d/boinc-client and its associated scripts suggests this should work, but it doesn't. The attempts I've read don't seem to have happy endings, either.

Has anyone actually succeeded in changing the data directory of the Linux BOINC client, and if so, how? Thanks for any help.

boinc does not seem to like changing the data directory
so you need to work around that one.
I tried 2 things, of which one worked.
What does not work: moving the data and use symlinks to link to the new directory. boinc does not see the data.

What does work: use mount --bind

[*] service boinc-client stop to stop the client(might be different on your system)
[*] mv /var/lib/boinc-client/* /path/to/new/dir/boinc-client/ move the data to the destination
[*] mount --bind /path/to/new/dir/boinc-client /var/lib/boinc-client bind the new directory to the old one
[*] now test it with service boinc-client start or your OS’s equivalent
[*] it will work, so add /path/to/new/dir/boinc-client /var/lib/boinc-client none bind 0 0 to your /etc/fstab so that the bind is created on system start

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I can attest to this solution.

I am running Fedora 18 with BOINC 7.0.29

I copied the contents of /var/lib/boinc (on a small SSD) to the hard drive where Ubuntu resides. Created an entry in fstab to mount the hard drive directory.

Next a shell script uses mount --bind to map the mount point + path on the hard drive to /var/lib/boinc

This takes the data, which could easily exceed 5-10GB off the SSD