On command line, I typed a command and hit enter. It doesn't output anything . How do I tell if it's running and not yet output, or it's asking for user input?

5 Answers

There's several approaches:

1. Try signalling end of input:Without superuser privileges it is hard to know what is going on underneath the hood. What can be done is to press Ctrl+d. Terminals and utilities in canonical mode send all available text to read() syscall upon receiving EOT signal bound to this key combination, and if there's no input - read() returns negative exit status which most utilities accept as signal to exit. Therefore, if a utility is waiting for input it will exit upon receiving the key combination. Otherwise, the utility is either running tasks or is not written properly.

2. Spying on syscalls:If you do have superuser privilege, you can run strace in another terminal to see what is currently being done. For that you need to find out PID of the program. For instance, in another terminal tab run pgrep -f firefox which may 1234 as example and then sudo strace -f -p 1234. If the output you see is stuck on read() syscall, it means the command probably is waiting for input. Otherwise, if you see syscalls running by, then command is doing something else. See a related question for usage of strace to also figure out if the long running command has exited.

3. Use command's own methods: Among other things, such utilities as dd use signals. For instance, if you use kill -USR1 1234 (where 1234 is PID of the running dd command), it will print to stdout the amount of bytes currently processed. Of course, this requires knowing about such behavior of the command in the first place. The above two methods are more general, and don't require deep knowledge of each command's behavior ( though it's always best to know what you're actually executing - otherwise you risk running a command which may do damage ).

How to tell if a program is running or wanting user input

It depends on the program and how you invoke it.

• Often but not always there will be a prompt, that indicates that the program is asking for input.

• If you are not sure, you can check if the program's process is busy

  • uses CPU - use top or htop

  • reads or writes - use sudo iotop -o

• And when the program has finished, you will see the shell's prompt.

Shellscript running

I had a shellscript that checks if a program is running, and now I have added the option -s to make it run sudo strace -f -p <PID> (according to Sergiy Kolodyazhnyy's answer) when a ... is found.

The shellscript uses

• ps -ef to find the majority of programs
• systemctl is-active --quiet to find some programs

• and if you wish strace in an xterm window.

  Install xterm if you want to use strace to watch the activity of a program.

Usage

$ ./running Usage: ./running <program-name> ./running <part of program name> Examples: ./running firefox ./running term # part of program name ./running dbus ./running 'dbus-daemon --session' # words with quotes ./running -v term # verbose output ./running -s term # strace checks activity 

You can install the shellscript running into a directory in PATH if you want easy access to it.

The shellscript code

#!/bin/bash # date sign comment # 2019-02-14 sudodus version 1.0 verbose=false strace=false if [ "$1" == "-v" ] then verbose=true shift fi if [ "$1" == "-s" ] then strace=true shift fi if [ $# -ne 1 ] then echo "Usage: $0 <program-name> $0 <part of program name> Examples: $0 firefox $0 term # part of program name $0 dbus $0 'dbus-daemon --session' # words with quotes $0 -v term # verbose output $0 -s term # strace checks activity" exit fi inversvid="\0033[7m" resetvid="\0033[0m" redback="\0033[1;37;41m" greenback="\0033[1;37;42m" blueback="\0033[1;37;44m" runn=false #tmpfil=$(mktemp) tmpdir=$(mktemp -d) tmpfil="$tmpdir/tmpfil" vtfile="$tmpdir/vtfile" vthead="$tmpdir/vthead" # check by systemctl systemctl is-active --quiet "$1" if [ $? -eq 0 ] then echo "systemctl is-active:" runn=true fi # check by ps ps -ef | tr -s ' ' ' ' | cut -d ' ' -f 8- | grep "$1" | grep -vE -e "$0 *$1" -e "$0 *.* *$1" -e "grep $1" | sort -u > "$tmpfil" #cat "$tmpfil" if $verbose || $strace then ps -ef |head -n1 > "$vthead" ps -ef | grep "$1" | grep -vE -e "$0 *.* *$1" -e "grep $1" | sort -u > "$vtfile" fi tmpstr=$(head -n1 "$tmpfil") #echo "tmpstr=$tmpstr" tmpess=$(grep -om1 "$1" "$tmpfil") #echo "tmpess=$tmpess" if [ "$tmpstr" == "$1" ] || [ "${tmpstr##*/}" == "$1" ] || [ "${1##*/}" == "${0##*/}" ] || [ "$tmpess" == "$1" ] then echo "ps -ef: active:" runn=true if $verbose then cat "$vthead" "$vtfile" fi elif test -s "$tmpfil" then if $runn then echo "----- consider also ------------------------------------------------------------" if $verbose then cat "$vthead" "$vtfile" else cat "$tmpfil" fi echo "--------------------------------------------------------------------------------" else echo "----- try with: ----------------------------------------------------------------" if $verbose then cat "$vthead" "$vtfile" else cat "$tmpfil" fi echo "--------------------------------------------------------------------------------" fi fi if $runn then echo -en "$greenback '$1" if [ "$tmpstr" != "$tmpess" ] then echo -n " ..." fi echo -e "' is running $resetvid" if $strace then which xterm if [ $? -eq 0 ] then pid=$(head -n1 "$vtfile" | sed 's/^ *//' | tr -s ' ' '\t' | cut -f 2) echo "checking pid=$pid; quit with 'ctrl + c' in the xterm window" xterm -title "'strace' checks '$1'" 2> /dev/null -e sudo strace -f -p $pid else echo "Please install 'xterm' for this function to work" exit fi fi else inpath=$(which "$1") if [ "$inpath" == "" ] then echo -e "$redback no path found to '$1' $resetvid" else echo -e "$blueback '$1' is not running $resetvid" fi fi rm -r "$tmpdir" 

Demo

Checking terminal windows in Lubuntu (LXTerminal started as x-terminal-emulator and custom gnome-terminal windows),

$ running -v -s term ----- try with: ---------------------------------------------------------------- UID PID PPID C STIME TTY TIME CMD sudodus 2087 1384 0 13:33 ? 00:00:00 x-terminal-emulator sudodus 2108 1269 0 13:33 ? 00:00:17 /usr/lib/gnome-terminal/gnome-terminal-server -------------------------------------------------------------------------------- no path found to 'term' $ running -v -s x-terminal-emulator ps -ef: active: UID PID PPID C STIME TTY TIME CMD sudodus 2087 1384 0 13:33 ? 00:00:00 x-terminal-emulator 'x-terminal-emulator' is running /usr/bin/xterm checking pid=2087; quit with 'ctrl + c' in the xterm window 

There is a lot of activity as soon as the cursor is in the terminal window.

Starting grep (waiting for input from /dev/stdin)

$ grep -i --color 'hello' asdf Hello World Hello World 

Checking it

$ running -s grep ps -ef: active: 'grep ...' is running /usr/bin/xterm checking pid=14982; quit with 'ctrl + c' in the xterm window 

There is not much activity, and you can identify what is happening.

If you're running the shell in a terminal, for example a terminal emulator or a typical ssh session, your shell has almost certainly enabled job control. This makes getting an answer to your question super easy in most cases.

Type Ctrl+Z to suspend the process and then bg to continue it in the background, then type an empty line to the shell so it'll check whether the program got stopped by a signal.

If the process is trying to read from the terminal, it will immediately get a SIGTTIN signal and will get suspended. (When job control is enabled, the system allows only one process at a time to read from the terminal.) The shell will report this. You can then type fg to continue the process in the foreground, and then type input to be read by the program as normal.

mp@ubuntu:~$ sleep 30 # a program that is not reading from the terminal ^Z [1]+ Stopped sleep 30 mp@ubuntu:~$ bg [1]+ sleep 30 & mp@ubuntu:~$ mp@ubuntu:~$ 

mp@ubuntu:~$ cat - # a program that is reading from the terminal ^Z [1]+ Stopped cat - mp@ubuntu:~$ bg [1]+ cat - & mp@ubuntu:~$ [1]+ Stopped cat - mp@ubuntu:~$ jobs -l [1]+ 3503 Stopped (tty input) cat - mp@ubuntu:~$ fg cat - hi hi 

Some programs, such as editors, will either trap or ignore the signal generated by Ctrl+Z or put the terminal into a mode where control characters don't even generate signals. You'll need to use more advanced techniques in this case, such as using strace to see if the process is doing read, select, poll, etc.

Not sure if you still need this, but still a useful trick to know: if the program seems to exit without any output you can check if it is running in background by executing

ps -efa | grep "program_name" 

Cheers!

Why not simply look at the column S (State) of the top command. If your program is waiting for input, there is a great chance it is sleeping and not running meaning top will output a S (for Sleeping this time) and not a R (for Running). Try this command as an example:

top -b -n 1 | sed -n '7,12p' | awk '{printf "%6s %-10s %-4s %-s\n",$1,$2,$8,$NF}'