root#test:/var/lib/tomcat/webapps/logs# ps aux | grep ppm
root 25522 0.0 0.0 1844 500 ? SN 14:13 0:00 sh -c /bin/bash -c "pdftoppm -f 1 -l 1 /pdf/input.pdf test/processing/output"
root 25523 49.6 0.7 18192 12620 ? RN 14:13 0:59 pdftoppm -f 1 -l 1 /pdf/input.pdf /test/processing/output
root 25539 0.0 0.0 2016 636 ? R+ 14:15 0:00 grep ppm
I am not familiar with this command. Why two processes are running I can't understand.
These are not two pdftoppm processes. The following is the pdftoppm process:
root 25523 49.6 0.7 18192 12620 ? RN 14:13 0:59 pdftoppm -f 1 -l 1 /pdf/input.pdf /test/processing/output
The following is the process for the shell command:
root 25522 0.0 0.0 1844 500 ? SN 14:13 0:00 sh -c /bin/bash -c "pdftoppm -f 1 -l 1 /pdf/input.pdf test/processing/output"
The first line in your grep output is for the shell command that was executed. The second line was for the actual pdftoppm invocation. The third line was for the grep. (Both your shell command and grep contained the string pdftoppm, which were a part of the process list when queried.)
The shell script is most likely excuted via a system call (that's what it would be in c). This system call invokes a command processor (PID 25522 in your case) to interpret the command.
The command itselves is the process with PID 25523.
In C the exec command family executes a command without invoking a command line interpreter.
Related
This question already has answers here:
How to get process ID of background process?
(9 answers)
Closed 1 year ago.
Below is the output of executing two commands ads2 svcd& and ps -aux|grep ads2
nvidia#nvidia-desktop:~$ ads2 svcd&
[1] 4593
nvidia#nvidia-desktop:~$ ps -aux|grep ads2
nvidia 4593 0.5 0.0 39796 23864 pts/0 Sl 08:20 0:00 /opt/ads2/arm-
linux64/bin/ads2svcd
nvidia 4603 0.0 0.0 6092 672 pts/0 S+ 08:20 0:00 grep --color=auto ads2
nvidia#nvidia-desktop:~$
nvidia#nvidia-desktop:~$
the command ads2 svcd& runs a process related to ads2 software. with ps -aux|grep ads2 i displayed the whole processes that contains the name "ads2".
Now What i'm trying to do is to get the process number of the ads2 which in this example is 4593. So i wrote the follwing bash script:
#!/usr/bin/env bash
process="$(ps -aux|grep ads | grep 'nvidia' | cut -d' ' -f 3)"
echo "The current ads2 process is " $process
The bash script outputs the following:
nvidia#nvidia-desktop:~$ ./test.sh
The current ads2 process is
As you see the process number is not filtered. So what i'm i doing wrong?
thanks in advance
List all the processes in the current shell with $$ built-in variable
ps --forest -gp $$
PID TTY STAT TIME COMMAND
3809 pts/1 Ss 0:01 bash
4896 pts/1 T 0:00 \_ vim file.json
22965 pts/1 S+ 0:00 \_ ssh dw
3607 pts/0 Ss 0:01 bash
2500 pts/0 R+ 0:00 \_ ps --forest -gp 3607
3327 tty2 Ssl+ 0:00 /usr/lib/gdm3/gdm-x-session --run-script i3
3329 tty2 Sl+ 8:12 \_ /usr/lib/xorg/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -background none -noreset -keeptty -verbose 3
3346 tty2 S+ 0:03 \_ i3
Just see the pid of them:
ps -opid --forest -gp $$
PID
3809
4896
22965
3607
2688
3327
3329
3346
If you need to use grep for any reason, use -opid,cmd with current shell:
ps -opid,cmd -gp $$ | grep vim
3851 grep --color=auto vim
4896 vim file.json
For all, just use -e
ps -e -opid,cmd | grep vim
4141 grep --color=auto vim
4896 vim file.json
The complete one, we have to ignore the grep itself:
ps -e -opid,cmd | grep vim | grep -v grep | cut -d' ' -f 2
4896
Without double grep using comm option for ps
ps -opid,comm -gp $$ | grep vim
4896 vim
of course the simplest one is pgrep
pgrep vim
4896
NOTE for variable assignment there should NOT be any space:
# wrong
ads2ProcessId = $(pgrep ads2)
# right
ads2ProcessId=$(pgrep ads2)
Problem: We use Zabbix as monitoring system. In addition to using its built in items, we also use something called external scripts feature (this), where custom scripts can be written and called via Zabbix. The problem facing here is its getting timed out. Script is simple expect file which goes inside a device and pulls some data. This works when called via root. But when called via Zabbix user, its complaining
/usr/bin/expect: /usr/bin/expect: cannot execute binary file
Script looks like this,
#!/usr/bin/expect
set host "IP_ADDRESS"
set uname "username"
set pwd "password"
set prompt "#|>|:|\\\$";
set val ""
set domain [lindex $argv 0]
log_user 0
set timeout -1
spawn /usr/bin/ssh "$uname#$host"
expect "$uname#$host's password:"
send "$pwd\n"
sleep 1
#expect -re "$prompt"
expect ">"
sleep 1
send "show wireless rf-domain statistics detail on $domain | grep Signals\r"
sleep 1
expect ">"
set val $expect_out(buffer)
send "exit\n"
puts $val
This is named as rf_signal.exp. Its called via a wrapper shell script named rf_signal.
#!/bin/bash
val=$(/usr/bin/expect '/usr/local/etc/scripts/rf_signal.exp' $1 | grep 'RF Signals' | cut -d':' -f2 | cut -d',' -f1 | cut -d' ' -f3 | sed -e 's/\s//g')
echo "$val"
And if called as root, this works fine for example
[root#zbx-proxy2 externalscripts]# pwd
/usr/local/share/zabbix/externalscripts
[root#zbx-proxy2 externalscripts]# whoami
root
[root#zbx-proxy2 externalscripts]# /usr/local/share/zabbix/externalscripts/rf_signal DOMAIN_NAME
241
[root#zbx-proxy2 externalscripts]#
Where as if I call as zabbix user I am getting, cannot execute binary file error. With expect as a path
[root#zbx-proxy2 externalscripts]# runuser -l zabbix /usr/bin/expect /usr/local/share/zabbix/externalscripts/rf_signal
/usr/bin/expect: /usr/bin/expect: cannot execute binary file
[root#zbx-proxy2 externalscripts]#
Without expect as a path, it waits -
[root#zbx-proxy2 externalscripts]# runuser -l zabbix /usr/local/share/zabbix/externalscripts/rf_signal
PSTree command output shows it calls expect and contents inside the file
[root#zbx-proxy2 ~]# pstree -p 26295
runuser(26295)---bash(26296)---bash(26309)-+-cut(26312)
|-cut(26313)
|-cut(26314)
|-expect(26310)---ssh(26316)
|-grep(26311)
`-sed(26315)
PS details.
[root#zbx-proxy2 ~]# ps aux | grep zabbix | grep -v "proxy\|agent\|fping"
root 26295 0.0 0.0 130700 1388 pts/3 S+ 15:46 0:00 runuser -l zabbix /usr/local/share/zabbix/externalscripts/rf_signal
zabbix 26296 0.0 0.0 108184 1628 pts/3 S+ 15:46 0:00 -bash /usr/local/share/zabbix/externalscripts/rf_signal
zabbix 26309 0.0 0.0 108184 576 pts/3 S+ 15:46 0:00 -bash /usr/local/share/zabbix/externalscripts/rf_signal
zabbix 26310 0.0 0.0 115336 2260 pts/3 S+ 15:46 0:00 /usr/bin/expect /usr/local/etc/scripts/rf_signal.exp
zabbix 26311 0.0 0.0 103260 868 pts/3 S+ 15:46 0:00 grep RF Signals
zabbix 26312 0.0 0.0 100972 676 pts/3 S+ 15:46 0:00 cut -d: -f2
zabbix 26313 0.0 0.0 100972 672 pts/3 S+ 15:46 0:00 cut -d, -f1
zabbix 26314 0.0 0.0 100972 676 pts/3 S+ 15:46 0:00 cut -d -f3
zabbix 26315 0.0 0.0 105268 872 pts/3 S+ 15:46 0:00 sed -e s/\s//g
zabbix 26316 0.0 0.0 59856 3220 pts/14 Ss+ 15:46 0:00 /usr/bin/ssh username#IP_ADDRESS
root 26688 0.0 0.0 105324 912 pts/7 S+ 15:47 0:00 grep zabbix
[root#zbx-proxy2 ~]#
All the scripts have read and execute permissions to all the users. And expect/grep/cut - whatever used inside the scripts are having read/execute permissions. What could be the issue?
I would suggest you use:
su - zabbix -c "/usr/local/share/zabbix/externalscripts/rf_signal"
to run the script instead of runuser.
Usually, the zabbix user has /sbin/nologin set up as a login shell, which means you won't be able to login via ssh onto the respective server. You may check /etc/passwd on the remote server to verify this.
As an additional note, you may use expect -d to enable debug in your expect script and see where it fails. Set expect's timeout to a different value like 180 (3 minutes) as opposed to -1 otherwise it will never exit.
I have a bash script (ScreamDaemon.sh) inside which a check that example of it isn't running already is added.
numscr=`ps aux | grep ScreamDaemon.sh | wc -l`;
if [ "${numscr}" -gt "2" ]; then
echo "an instance of ScreamDaemon still running";
exit 0;
fi
Normally, if there are no another copy of script running, ps aux | grep ScreamDaemon.sh | wc -l should return 2 (it should find itself and grep ScreamDaemon.sh), but it returns 3.
So, I try to analyse what happens and after adding some echoes see this:
there are lines I have added into the script
ps aux | grep ScreamDaemon.sh
ps aux | grep ScreamDaemon.sh | wc -l
str=`ps aux | grep ScreamDaemon.sh`
echo $str
numscr=`ps aux | grep ScreamDaemon.sh | wc -l`;
echo $numscr
there is an output:
pamela 27894 0.0 0.0 106100 1216 pts/1 S+ 13:41 0:00 /bin/bash ./ScreamDaemon.sh
pamela 27899 0.0 0.0 103252 844 pts/1 S+ 13:41 0:00 grep ScreamDaemon.sh
2
pamela 27894 0.0 0.0 106100 1216 pts/1 S+ 13:41 0:00 /bin/bash ./ScreamDaemon.sh pamela 27903 0.0 0.0 106100 524 pts/1 S+ 13:41 0:00 /bin/bash ./ScreamDaemon.sh pamela 27905 0.0 0.0 103252 848 pts/1 S+ 13:41 0:00 grep ScreamDaemon.sh
3
I also tried to add the sleep command right inside `ps aux | grep ScreamDaemon.sh; sleep 1m` and see from the parallel terminal how many instances ps aux|grep ScreamDaemon.sh shows:
[pamela#pm03 ~]$ ps aux | grep ScreamDaemon.sh
pamela 28394 0.0 0.0 106100 1216 pts/1 S+ 14:23 0:00 /bin/bash ./ScreamDaemon.sh
pamela 28403 0.0 0.0 106100 592 pts/1 S+ 14:23 0:00 /bin/bash ./ScreamDaemon.sh
pamela 28408 0.0 0.0 103252 848 pts/9 S+ 14:23 0:00 grep ScreamDaemon.sh
So, it seems that
str=`ps aux | grep ScreamDaemon.sh`
contrary to
ps aux | grep ScreamDaemon.sh
found two instances of ScreamDaemon.sh, but why? Where this additional copy of ScreamDaemon.sh come from?
This is an output of pstree -ap command
│ ├─sshd,27806
│ │ └─sshd,27808
│ │ └─bash,27809
│ │ └─ScreamDaemon.sh,28731 ./ScreamDaemon.sh
│ │ └─ScreamDaemon.sh,28740 ./ScreamDaemon.sh
│ │ └─sleep,28743 2m
Why can a single bash script show up multiple times in ps?
This is typical when any constructs which implicitly create a subshell are in play. For instance, in bash:
echo foo | bar
...creates a new forked copy of the shell to run the echo, with its own ps instance. Similarly:
( bar; echo done )
...creates a new subshell, has that subshell run the external command bar, and then has the subshell perform the echo.
Similarly:
foo=$(bar)
...creates a subshell for the command substitution, runs bar in there (potentially exec'ing the command and consuming the subshell, but this is not guaranteed), and reads its output into the parent.
Now, how does this answer your question? Because
result=$(ps aux | grep | wc)
...runs that ps command in a subshell, which itself creates an extra bash instance.
How can I properly ensure that only one copy of my script is running?
Use a lockfile.
See for instance:
How to prevent a script from running simultaneously?
What is the best way to ensure only one instance of a Bash script is running?
Note that I strongly suggest use of a flock-based variant.
Of course, the reason you find an additional process is because:
One process is running the sub-shell (of the command execution `..`)
included in your line: numscr=`ps aux | grep ScreamDaemon.sh | wc -l`;
that's the simplest answer.
However I would like to make some additional suggestions about your code:
First, quote your expansions, it should be: echo "$str".
Not doing so is making several lines collapse into a long one.
Second, you may use: grep [S]creamDaemon.sh to avoid matching the grep command itself.
Third, capture the command just once in a variable, then count lines from the variable. In this case it presents no problem, but for dynamic processes, one capture and the following capture to count could give different results.
Fourth, make an habit of using $(...) command substitutions instead of the more error prone (especially when Nesting) `...`.
### Using a file as the simplest way to capture the output of a command
### that is running in this shell (not a subshell).
ps aux | grep "[S]creamDaemon.sh" > "/tmp/tmpfile$$.txt"
str="$(< "/tmp/tmpfile$$.txt")" ### get the value of var "str"
rm "/tmp/tmpfile$$.txt" ### erase the file used ($$ is pid).
numscr="$(echo "$str" | wc -l)" ### count the number of lines.
echo "$numscr" ### present results.
echo "$str"
str="$( ps aux | grep "[S]creamDaemon.sh" )" ### capture var "str".
numscr="$(echo "$str" | wc -l)" ### count the number of lines.
echo "$numscr" ### present results.
echo "$str"
### The only bashim is the `$(<...)`, change to `$(cat ...)` if needed.
#CharlesDuffy covered the point of a flock quite well, please read it.
bash: 4.3.42(1)-release (x86_64-pc-linux-gnu)
Executing the following script:
# This is myscript.sh
line=$(ps aux | grep [m]yscript) # A => returns two duplicates processes (why?)
echo "'$line'"
ps aux | grep [m]yscript # B => returns only one
Output:
'tom 31836 0.0 0.0 17656 3132 pts/25 S+ 10:33 0:00 bash myscript.sh
tom 31837 0.0 0.0 17660 1736 pts/25 S+ 10:33 0:00 bash myscript.sh'
tom 31836 0.0 0.0 17660 3428 pts/25 S+ 10:33 0:00 bash myscript.sh
Why does the inline executed ps-snippet (A) return two lines?
Summary
This creates a subshell and hence two processes are running:
line=$(ps aux | grep [m]yscript)
This does not create a subshell. So, myscript.sh has only one process running:
ps aux | grep [m]yscript
Demonstration
Let's modify the script slightly so that the process and subprocess PIDs are saved in the variable line:
$ cat myscript.sh
# This is myscript.sh
line=$(ps aux | grep [m]yscript; echo $$ $BASHPID)
echo "'$line'"
ps aux | grep [m]yscript
In a bash script, $$ is the PID of the script and is unchanged in subshells. By contrast, when a subshell is entered, bash updates $BASHPID with the PID of the subshell.
Here is the output:
$ bash myscript.sh
'john1024 30226 0.0 0.0 13280 2884 pts/22 S+ 18:50 0:00 bash myscript.sh
john1024 30227 0.0 0.0 13284 1824 pts/22 S+ 18:50 0:00 bash myscript.sh
30226 30227'
john1024 30226 0.0 0.0 13284 3196 pts/22 S+ 18:50 0:00 bash myscript.sh
In this case, 30226 is the PID on the main script and 30227 is the PID of the subshell running ps aux | grep [m]yscript.
a command substitution ($(...))
each segment of a pipeline[1]
cause Bash to create a subshell (a child process created by forking the current shell process), but then Bash optimizes away subshells if they result in a single call to an external utility.
(What I think is happening in the optimization scenario is that a subshell is actually created but then instantly replaced by the external utility's process, via something like exec. Do let me know if you know for sure.)
Applied to your example:
line=$(ps aux | grep [m]yscript) creates 3 child processes:
1 subshell - the fork of your script you see as an additional match returned by grep.
2 child processes (1 for each pipeline segment) - ps and grep; they take the place of the optimized-away subshells; their parent process is the 1 remaining subshell created by the command substitution.
ps aux | grep [m]yscript creates 2 child processes (1 for each pipeline segment):
ps and grep; they take the place of the optimized-away subshells; their parent process is the current shell.
For an overview of the scenarios in which a subshell is created in Bash, see this answer of mine, which, however, doesn't cover the optimizing-away scenarios.
[1] In Bash v4.2+ you can set option lastpipe (off by default) in order to make the last pipeline segment run in the current shell instead of a subshell; aside from a slight efficiency gain, this allows you to declare variables in the last segment that the current shell can see after the pipeline exits.
I am trying to find the PID of a process (motion_sensor.py), but pgrep returns nothing. Why does it not return the process id?
pgrep -u www-data motion_sensor.py
ps -ef | grep "motion_sensor" returns
root 7149 1 93 Apr25 ? 15:59:08 python motion_sensor.py
www-data 31872 23531 0 14:09 ? 00:00:00 sh -c sudo python /home/pi/Desktop/PiControl/motion_sensor.py
root 31873 31872 0 14:09 ? 00:00:00 sudo python /home/pi/Desktop/PiControl/motion_sensor.py
root 31874 31873 47 14:09 ? 00:14:30 python /home/pi/Desktop/PiControl/motion_sensor.py
pi 32645 32202 0 14:39 pts/0 00:00:00 grep --color=auto motion_sensor.py
Normally pgrep applies the search pattern to process names. The process name in this case is python and not motion_sensor.py. If you want to grep for the full path rather than just the process name you need to pass -f:
pgrep -u www-data -f motion_sensor.py
Check man pgrep
the requirement is to find out PID of a process,
So you can try :
ps aux | grep www-data motion_sensor.py