Uninterruptible sleep
From Linux Developer's Documentation
A process is in an uninterruptible sleep (marked by the "D" letter in the process state[1]) when it it waiting in the kernel code for hardware I/O. This wait is uninterruptible because canceling it might cause data loss or hardware getting into inconsistent state.
A process in this state cannot immediately react on signals (not even on SIGKILL), but the signals are queued and will take effect after the process leaves the uninterruptible sleep.
[edit] Notes
- ↑ The "D" letter is a shortcut for "Disk", as this traditionally occurred when waiting for a slow disk I/O.
