In computing, a status key is a keyboard key that causes an operating system and/or a program to output status information on a terminal when it is pressed. In the event that a program on a terminal produces no indications that it is running, typing the status key will reveal the program's state and activity.[1] Older implementations produced only a quick one-line status report for the current job when the status key was pressed.[2] Newer implementations support sending a signal to the current process to allow the application to report on status as well.[3]
Operating system-level implementations
Several different operating systems have a status key feature implemented in the kernel or other low-level component.
TENEX
TENEX has the feature since at least 1971: "Another terminal Interrupt character, control-T is serviced by the EXEC. It interrupts a user's EXEC process to type out total CPU and console time used, and status of the fork being run under the EXEC."[4]
DEC RSTS/E
RSTS/E is documented as having a status key at least as far back as 1977 and it continued to have one into at least the 1980s. Typing the status key results in output that is represented by the following example:[5][6][2]
On TOPS-10 when the CTRL/T (control-T) key is pressed, the monitor prints status information pertaining to the job on the terminal. Typing CTRL/T displays a job's progress without interrupting its execution. No representation of a control-t character is displayed on the terminal, just the status information.[7]
DAY: :05:43 RUN:0.48 RD:75 WR:8 SOS 12+19p ^C Ctx:1 PC:400275
Incremental values in the table below indicate that the value is the accumulation since login or last CTRL/T whichever was shortest.[7]
Field
Value
Incremental day time
DAY: :05:43
Incremental run time
RUN:0.48
Incremental disk reads
RD:75
Incremental disk writes
WR:8
Program name
SOS
Amount of memory program is using
12+19p
Context number
Ctx:1
Job state code
^C
Program Counter
PC:400275
Job state, INPUT WAIT or OUTPUT WAIT
(only when CTRL/T is used at USER level)
DEC TOPS-20
TOPS-20 reports a shorter list of information than its predecessors:[9]
09:36:35 TEST Running at 404157 Used 0:00:35.8 in 0:30:39, Load 4.04
Field
Value
Time
09:36:35
Name
TEST
Status
Running at 404157
Used CPU-time
Used 0:00:35.8
Logged-in-time
in 0:30:39
Load average
Load 4.04
MIT ITS
ITS copied the idea from TOPS-20,[10] but used the key sequence Control+_J.[11]
19:29:10 3 RMS HACTRN EMACS1 130566
Field
Value
Time
19:29:10
Job index
3
User name
RMS
Job name
HACTRN
System name
EMACS1
User program counter
130566
VSI OpenVMS
OpenVMS has a status key which can be customized and works with remote processes.[12] The default output includes these items:[1]
Because XNU has a FreeBSD kernel which has been modified to be a Mach server process, the terminal driver includes a status key which is inherited.[19][20][21][22]
load: 3.04 cmd: sleep 719 waiting 0.00u 0.00s
Field
Value
Five minute load average
load: 3.04
Command name
cmd: sleep
Process ID
719
Wait channel name or lock name
waiting
Elapsed user CPU time
0.00u
Elapsed system CPU time
0.00s
Application-level implementations
It addition to implementing a status key in the kernel or related OS component, some applications have features that allow you to press a key to view the application's status.
SDS-940 running BBN Lisp in 1969
BBN Lisp which runs on an SDS 940 had a status key which was implemented in the Lisp which ran on an OS, rather than in the OS kernel itself.[23]
Control-T
Print Time. Causes an immediate
printout of the total execution time
(in clock ticks) for the job, (even
during garbage collections), i.e.
clock[2], (p. 14.22). A series of
such printouts should show increasing
numbers if the program is using any
CPU time. Of course, the program is
not using CPU time if it is waiting
for input. This information may
serve to help the user determine if
his LISP and/or the time sharing sys-
tem has crashed.
^Peleg, Guy (2006-10-01). "OpenVMS Utilties Update"(PDF). OpenVMS News. Bruden On Shore Systems Group. Archived(PDF) from the original on 2017-12-06. Retrieved 2017-11-06.
^Karels, Michael J. (1989-08-26). "Computer Systems Research Group BSD Distribution signal.h 7.5". SCCS to fossil conversion of the original University of California, Berkeley Computer Systems Research Group BSD repository. Regents of the University of California. Retrieved 2017-12-05. #define SIGINFO 29 /* information request */
^Teitelbaum, Marc (1989-10-26). "Computer Systems Research Group BSD Distribution tty.c 7.18". SCCS to fossil conversion of the original University of California, Berkeley Computer Systems Research Group BSD repository. Regents of the University of California. Retrieved 2017-12-05. add ^T prototype
^Teitelbaum, Marc (1990-05-01). "Computer Systems Research Group BSD Distribution tty.c 7.22". SCCS to fossil conversion of the original University of California, Berkeley Computer Systems Research Group BSD repository. Regents of the University of California. Retrieved 2017-12-05. ^T
