SG_GET_TIMEOUT 0x2202. Ignores its 3rd argument and _returns_ the timeout value (which will be >= 0 ). The unit of this timeout is "jiffies" which are currently 10 millisecond intervals on i386 (less on an alpha). Linux supplies a manifest constant HZ which is the number of "jiffies" in 1 second. This ioctl() is not relevant to the sg version 3 driver because timeouts are specified explicitly for each command in the sg_io_hdr structure.