Qt client not exiting on Linux I am running Ubuntu 12.04. When I close bitcoin-qt (or any of its derivatives, like litecoin-qt or dogecoin-qt), sometimes it does not completely exit. I then have to run killall -9 bitcoin-qt, or sometimes when even that doesn't work, killall -9 bitcoin-shutoff (apparently the client calls a bitcoin-shutoff process to shut itself down). I am wondering if there is a fix for this, to prevent the client from refusing to close in the future.
Have you set a proxy?

From my experience slow shutdown seems to have to do with slow proxies (for example, Tor).
There is an issue for this: https://github.com/bitcoin/bitcoin/issues/2954

If it is not the network thread that hangs, but database synchronization, then killing with -9 can be dangerous. 

I'd suggest debugging this by running in gdb, Ctrl-Cing when it hangs, and then getting backtraces for every still-running thread.