This question already has answers here:
Whats the difference between redirections "1>/dev/null 2>&1" and " 2>&1 1>/dev/null"?
(3 answers)
Closed 2 years ago.
For me, the following two bash commands produce different results:
# returns instantly
ssh localhost 'nohup sleep 5 >out 2>&1 &'
# returns after 5 seconds
ssh localhost 'nohup sleep 5 2>&1 >out &'
It's surprising because the following two bash commands produce the same result:
# both return instantly
nohup sleep 5 >out 2>&1 &
nohup sleep 5 2>&1 >out &
Why?
This form:
command >out 2>&1
... takes standard out and puts it to a file. It then takes standard error and puts it to the same location as standard out. Both streams are sent to a file.
This form:
command 2>&1 >out
... takes standard error and puts it on standard out. It then takes what would be sent to standard out and sends it to a file. It does not send standard error to the file.
So, at your terminal, you are backgrounding the task and the prompt returns immediately. When using ssh, in the first case, there is no output to display because everything has been sent to a file. In the other case, standard out can still display information that the application tries to send to standard error.
My expectation is that ssh returns immediately in the first case because there will never by any output. In the second case, there is an open stream that may return data for you to see.
Related
I'm wrote a bash script and I don't have a chance to download pssh. However, I need to run multiple ssh commands in parallel. There is no problem so far, but when I run ssh commands, I want to see the outputs sequentially from the remote machine. I mean one ssh has multiple outputs and they get mixed up because more than one ssh is running.
#!/bin/bash
pid_list=""
while read -r list
do
ssh user#$list 'commands'&
c_pid=$!
pid_list="$pid_list $c_pid"
done < list.txt
for pid in $pid_list
do
wait $pid
done
What should I add to the code to take the output unmixed?
The most obvious way to me would be to write the outputs in a file and cat the files at the end:
#!/bin/bash
me=$$
pid_list=""
while read -r list
do
ssh user#$list 'hostname; sleep $((RANDOM%5)); hostname ; sleep $((RANDOM%5))' > /tmp/log-${me}-$list &
c_pid=$!
pid_list="$pid_list $c_pid"
done < list.txt
for pid in $pid_list
do
wait $pid
done
cat /tmp/log-${me}-*
rm /tmp/log-${me}-* 2> /dev/null
I didn't handle stderr because that wasn't in your question. Nor did I address the order of output because that isn't specified either. Nor is whether the output should appear as each host finishes. If you want those aspects covered, please improve your question.
I'd like to run a linux console command from a terminal, preventing it from accessing the TTY by itself (which will, for example, happen often when the console command tries to request a password from the user - this should just fail). The closest I get to a solution is using this wrapper:
temp=`mktemp -d`
echo "$#" > $temp/run.sh
mkfifo $temp/out $temp/err
setsid sh -c "sh $temp/run.sh > $temp/out 2> $temp/err" &
cat $temp/err 1>&2 &
cat $temp/out
rm -f $temp/out $temp/err $temp/run.sh
rmdir $temp
This runs the command as expected without TTY access, but passing the stdout/stderr output through the FIFO pipes does not work for some reason. I end up with no output at all even though the process wrote to stdout or stderr.
Any ideas?
Well, thank you all for having a look. Turns out that the script already contained a working approach. It just contained a typo which caused it to fail. I corrected it in the question so it may serve for future reference.
This question already has answers here:
Call a function using nohup
(6 answers)
Closed 4 years ago.
I'm not sure this is really possible, but maybe someone has some suggestion on how I can do something similar to this:
#!/bin/bash
dissed() {
for i in {1..10}
do
sleep 5
echo "$(date)"
done
}
/usr/bin/screen -S disowned -d -m dissed & disown -h;
screen -ls
echo "done."
Of course this doesn't work, since I assume the function gets killed when the script ends. I know it works when I substitute an actual .sh file where the "dissed" function gets called, but this is what I want to avoid.
Is there some way to disown a function or subscript located in the parent?
To detach a process from a bash script:
nohup ./process &
If you stop your bash script with SIGINT for instance, the process won't be bothered and will continue to execute normally. stdout & stderr will be redirected to a file: nohup.out.
If you wish to execute a detached command while being able to see the output in the terminal, then use tail:
TEMP_LOG_FILE=tmp.log
"$TEMP_LOG_FILE"
nohup ./process &> "$TEMP_LOG_FILE" & tail -f "$TEMP_LOG_FILE" &
This is the first question that I post here. I tried to do a throughout search, but if I haven't (and the answer is obvious somewhere else), please just let me know.
I have a script that runs a program for me, here it is:
csv_file=../data/teste_nohup.csv
trace_file=../data/gnp.trace
declare -i n=100
declare -i p=1
declare -i counter=0
while [ $counter -lt 3 ];
do
n=100
while true
do
nice -19 sage gnptest.py ${n} ${p} | tee -a ${csv_file}
notify-send "finished test gnp ${n} ${p}"
done
done
So, what I'm trying to do is run the gnptest.py program a few times, and have the result be written to the csv_file.
The problem is, that depending on the input, the program may take a long time to complete. So I'd like to connect to the server over ssh, start the program, close the terminal, and check the output file from time to time.
I've tried nohup and disown. Nohup creates a huge nohup.out file, full with errors that I don't get while normally running the script (it complains about using the -lt operand, for example). But the biggest problem that I'm facing is that no command (nohup ou disown -h) is executing the program and sending the output to the file that I've specified in the csv_file variable, which is being done using the tee command. Also, none of them seem to continue running after I logout...
Any help will be much appreciated.
Thanks in advance!!
i hv just joined so cannt add comment
Please try by using redirection instead of tee in script
And to get rid of Nohup.out use following to run script
nohup script.sh > /dev/null 2>&1 &
If above produces error use
nohup script.sh > /dev/null 2>&1 </dev/null &
Hope this will help.
I have a basic script that outputs various status messages. e.g.
~$ ./myscript.sh
0 of 100
1 of 100
2 of 100
...
I wanted to wrap this in a parent script, in order to run a sequence of child-scripts and send an email upon overall completion, e.g. topscript.sh
#!/bin/bash
START=$(date +%s)
/usr/local/bin/myscript.sh
/usr/local/bin/otherscript.sh
/usr/local/bin/anotherscript.sh
RET=$?
END=$(date +%s)
echo -e "Subject:Task Complete\nBegan on $START and finished at $END and exited with status $RET.\n" | sendmail -v group#mydomain.com
I'm running this like:
~$ topscript.sh >/var/log/topscript.log 2>&1
However, when I run tail -f /var/log/topscript.log to inspect the log I see nothing, even though running top shows myscript.sh is currently being executed, and therefore, presumably outputting status messages.
Why isn't the stdout/stderr from the child scripts being captured in the parent's log? How do I fix this?
EDIT: I'm also running these on a remote machine, connected via ssh using pseudo-tty allocation, e.g. ssh -t user#host. Could the pseudo-tty be interfering?
I just tried your the following: I have three files t1.sh, t2.sh, and t3.sh all with the following content:
#!/bin/bash
for((i=0;i<10;i++)) ; do
echo $i of 9
sleep 1
done
And a script called myscript.sh with the following content:
#!/bin/bash
./t1.sh
./t2.sh
./t3.sh
echo "All Done"
When I run ./myscript.sh > topscript.log 2>&1 and then in another terminal run tail -f topscript.log I see the lines being output just fine in the log file.
Perhaps the things being run in your subscripts use a large output buffer? I know when I've run python scripts before, it has a pretty big output buffer so you don't see any output for a while. Do you actually see the entire output in the email that gets sent out at the end of topscript.sh? Is it just that while the processes run you're not seeing the output?
try
unbuffer topscript.sh >/var/log/topscript.log 2>&1
Note that unbuffer is not always available as a std binary in old-style Unix platforms and may require a search and installation for a package to support it.
I hope this helps.