A process is an instance of a computer program that is being executed.

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Why does “kill -9 0” end my console session?

I just wonder why kill -9 0 ends my tty console session? What exactly is PID 0, it is not listed on a ps aux?
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Launch process as another user/group (in init.d script)

I am editing a init.d script. The init.d script runs a utility script which then runs an process. From either bash scripts how would I make it launch the main process as a specific user and group?
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How can I tell when a process has finished writing to a file?

I have a process which has been spawned from a shell. It is running as a background process and exporting a DB to a CSV file in /tmp. How can I tell when the background process has completed ...
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Harddrive I/O per Pid

is there any way to see the disk I/O per pid/process ? Monitorix shows me the following and correct me if I´m wrong, but it looks like that the harddrive is slowing down the whole system: UPDATE #1 ...
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What does kill 0 do actually?

In the man page, it says: kill [ -s signal | -p ] [ -a ] [ -- ] pid ... pid... Specify the list of processes that kill should signal. Each pid can be one of five things: 0 All ...
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Execute Nohup command with input

In UNIX, I have a process that I want to run using nohup. However this process will at some point wait at a prompt where I have to enter yes or no for it to continue. So far, in UNIX I have been doing ...
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388 views

What three files are always opened by a process?

Someone mentioned that there are three different files that a process always opens. What does this mean? What files are they?
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950 views

What's the purpose of the /proc/pid/mountinfo file?

What's the purpose of the /proc/pid/mountinfo file (with pid being numerical process id)? As far as I can see it reflects contents of the /proc/mounts file but with added information. Also the file ...
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Simulate an unkillable process in D state

For catastrophe testing scenarios on out server environment we're looking for an easy way to make a process stuck in D (uninterruptible sleep) state. Any easy ways? An example C sample code would be ...
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Elegantly get list of children processes

I would like to get a list of all the processes whose parent is $pid. This is the simplest way I've come up with: pstree -p $pid | tr "\n" " " |sed "s/[^0-9]/ /g" |sed "s/\s\s*/ /g" Is there any ...
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How to kill a daemon with its name gracefully?

I usually kill a process with killall. killall markdoc But I am not sure if this command terminates the process gracefully. Does this command achieve graceful termination? If it does not, how can ...
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Finding out with which parameters a program was started

Is there a way to find out for any given process with which parameters it was started?
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Dump process core without killing the process

Is there a way to get a core dump (or something similar) for a process without actually killing the processes? I have a multithreaded python process running on an embedded system. And I want to be ...
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How can I create a hard to kill process

I want to create a program that will be difficult to stop (even for the administrator) once it is started (with root privileges). Once started the process should continue to start itself at startup ...
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953 views

Why is I/O uninterruptible?

What is the rationale behind making I/O uninterruptible? What would be the negative consequences if a process handling I/O were allowed to handle a signal?
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983 views

How to find tty from which a particular cmd “scp” is executed

How can I find out who executed a particular command and which terminal was used to run it? Original: how can i know particular cmd is executed by whom and to know about my terminal
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Understanding top and load average

I'm observing a high load average on a certain machine (about 9) in all three load fields. I understand load as the number of processes in state "run" / currently desiring CPU time. Am I correct at ...
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How to check, which limit was exceeded? (Process terminated because of ulimit. )

Let's assume process runs in ulimited environment : ( ulimit ... -v ... -t ... -x 0 ... ./program ) Program is terminated. There might be many reasons : memory/time/file limit exceeded ; just ...
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481 views

What should interactive shells do in orphaned process groups?

(Re-posting in unix per the suggestion in http://stackoverflow.com/questions/13718394/what-should-interactive-shells-do-in-orphaned-process-groups) The short question is, what should a shell do if it ...
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Is the sum of all PIDs “utime” the total system utime?

In order to measure a user's total CPU time, I'm using the "utime" field out of /proc/[pid]/stat: utime %lu Amount of time that this process has been scheduled in user mode, measured in ...
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Why file-nr and lsof count on open files differs?

I am running into a problem all of a sudden; all my applications and the server was running fine and all of a sudden I see the number of open files shoot up. I am checking it with this command: cat ...
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578 views

How to determine what instructions a process is executing?

I know about strace and ltrace, but that only tells me what system calls and library calls a process is executing, respectively. I would like to know exactly what instructions a process is executing. ...
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Terminating a bash shell script running in the background

I often use bash shell scripts to run simple commands for many different files. For example, suppose that I have the following bash shell script, called script.sh, that runs the program/command foo ...
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How to stop a bunch of processes on unix fast?

How to stop a bunch of processes on unix fast. I can use ps/top, kill. If the number of processes is very large, I use shell script. Are there other ways, only one or two unix commands can do it ...
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Kill only one Java process

I usually run few Java applications, one for server running locally and other for some IDE like NetBeans. And from time to time, after lots of redeployments, my server get stuck on ...
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How do Linux permissions work when a process is running as a specific group?

This is something I haven't been able to find much info on so any help would be appreciated. My understanding is thus. Take the following file: -rw-r----- 1 root adm 69524 May 21 17:31 ...
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In bash script, how to capture stdout line by line

In a bash script, I would like to capture the standard output of a long command line by line, so that they can be analysed and reported while initial command is still running. This is the complicated ...
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If I see a process running using ps, how can I find the executable?

If I can see a process running using ps -e, how can I find the file which launched it?
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How can I allow a user to prioritize a process to negative niceness?

I want a user to run a specific process on the system with a negative nice value. I can't simply fork the process to background as this specific program is a minecraft server and I rely on the command ...
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Bash way to check if a process is already running in the background (and skip re-execution based on that)?

Can I make a bash command line that only runs a certain command if the process is not already running (in the background)? How do I check*, if a command is already running? (so I can add the next ...
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What is “automatic stack expansion”?

getrlimit(2) has the following definition in the man pages: RLIMIT_AS The maximum size of the process's virtual memory (address space) in bytes. This limit affects calls to brk(2), mmap(2) and ...
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Simple queuing system?

Given a commodity PC, we would like to use it to execute some tasks in the background round the clock. Basically, we would like to have commands like: add-task *insert command here* list-tasks ...
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Viewing foreground process using ps

I can see the background process using ps. But Is there a way to view the foreground process? For example, $nohup process1 & then ps -ef | grep "process1" would display the process ...
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Real time priorities in non real time OS

If I do the following command on my standard Linux Mint installation: comp ~ $ ps -eo rtprio,nice,cmd RTPRIO NI CMD ... 99 - [migration/0] 99 - [watchdog/0] 99 - [migration/1] - 0 ...
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How to view summaric memory usage of groups of commands (instead of processes)

Is there a way to group similar processes when using tools like top/htop? Sometimes I just want to know whats eating my memory and some programs (browsers mostly) are using multiple processes, which ...
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ATOP shows red line vmcom and vmlim. What does it mean?

utility atop shows: ATOP - MyServer 2013/01/07 00:03:57 10 seconds elapsed PRC | sys 2.18s | user 8.33s | #proc 141 | #zombie 0 | #exit 0 | CPU | sys 21% | ...
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Silently start task in background

I know that you can use this to start a process in the background, without getting the notification when the process is put in the background and when it is done like so: (command &) &> /dev/null ...
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How can you determine which process scheduler is being used? [duplicate]

I.e. is it the O(1) scheduler, the CFS scheduler, or an older one?
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How to enable random PIDs on Linux?

I'm currently comparing random PID implementation on OpenBSD, FreeBSD and Linux from security perspective. As long as OpenBSD and FreeBSD are concerned, my work is done. However, while the answer ...
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955 views

Kill user processess on logout

I have a Ubuntu server that handles remote X sessions from users. However, I don't want to allow users to run any kind of background processes - so here is my question: How do I prevent users from ...
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Which of the following codes will run in the same process of the current shell

A. { echo "Hello World"; } >outputfile B. ( echo "Hello World" ) >outputfile C. ./anothershell.sh D. /bin/echo "Hello World" Which is right? And what kind of command can run in the same ...
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Graceful way to kill process

After my bash script is done with the selenium server, the script kills it like this: kill `ps -ef | grep selenium | awk '{ print $2 }'` While this works and it does kill the selenium script, it ...
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634 views

How does getpid work?

The getpid system call returns the process id of the invoking process. How does the kernel figure out which process is invoking the system call ?
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How to kill a process which can't be killed without rebooting?

There are 5 processes which can't be killed by kill -9 $PID and executing cat /proc/$PID/cmdline will hang the current session. Maybe they're zombie processes. Executing ps -ef or htop will also hang ...
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Finding the ID of a process and killing it

When ever I need to kill a background process I do ps -e | grep <process_name> Which prints something like this 1766 ? 00:00:13 conky , Then I use the process ID to kill it like so kill 1766 . ...
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Running continuous jobs remotely

I'm new to Linux, and I'm probably asking a fairly basic question. How do I run a continuous program on Linux? Basically, I have a program that will continuously check for content on a website. This ...
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chdir(<directory>) doesn't change directory after exiting to shell

I wanted to make a simple C program to change to my project directory. Its content is as follows: #include <unistd.h> int main() { chdir("/home/enedil/projects/algo"); return 0; } I ...
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Threads vs (Forked) Processes

Linux applications generally fork then exec (with execve() ), but Java applications, and certain Apache MPMs use threading. If forking, uses the fork + exec to spawn a process, what is the high level ...
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Understanding environmental variables in different contexts

Trying to understand the behaviour of the environment in Linux (Ubuntu 13.04 concretely), I've find different situations where setting envirionment variables are used or defined for/in different ...
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killall gives me `no process found ` but ps

Could somebody explain to me the difference between kill and killall? Why doesn't killall see what ps shows? # ps aux |grep db2 root 1123 0.0 0.8 841300 33956 pts/1 Sl 11:48 0:00 ...