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

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What does <defunct> mean in the output of ps?

I had issued the ps -ef|grep java command and this is one of the entries that I got : subhrcho 875 803 0 Jan23 pts/5 00:02:27 [java] <defunct> What is <defunct> implying here ? ...
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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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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 mremap(...
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How to check which process is using most memory

When I check free in one of Prod server it showing 70% of memory is being used: total used free shared buffers cached Mem: 164923172 141171860 23751312 ...
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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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Running multiple nohup commands in background

Got two commands cmd1 and cmd2. Of the two, cmd2 takes longer to finish. Need to run cmd2 and then cmd1. Tried to run them in following way: bash$ (nohup ./cmd2>result2 &) && nohup ....
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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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What is meant by “Unknown instance” when restarting a service?

I am trying to get vsftpd file server running on Ubuntu 13.10, I'm unable to connect to the server from another network, although this other network is connected to the server's network and ping is ...
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How can I get the wall clock time of a running process?

I started a hash check of a large file and don't want to restart it using time. How can I get the wall clock time without using time at the beginning or using date right before I invoke a command?
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Will process ids be recycled? What if you reach the maximal id?

Process IDs are strictly increasing, but if your system runs long enough and there is a lot of processes terminating and starting, you could at some point reach the limit of the underlying integral ...
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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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How do I determine if a program is running when I start a shell and start that program if it is not already running?

When I start a shell, in my case bash and/or zsh, what lines do I need to add to .zshrc and/or .bashrc to check to see if a program is already running, and if the program is not already running, start ...
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Why do top and ps show different PIDs for the same processes?

When I run top -H, I see that my multiple mysql threads all have the same PID. However, in ps -eLf I see each one has a different PID: ps -eLf UID PID PPID LWP C NLWP STIME TTY ...
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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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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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Getting disk i/o statistics for single process in Linux

I need to monitor the I/O statistics of a process that writes to disk. The purpose is to avoid write rates too high for long periods. I know there's iostat tool to accomplish this task on a system-...
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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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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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Suggestions needed to debug why ps -ef gets stuck

A few of my processes consume 100% cpu. I'm trying to figure out which scripts are causing it I tried running strace ps -ef: open("/proc/PID/status", O_RDONLY) = 6 read(6, "Name:\textract\nState:\tR ...
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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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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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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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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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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 ...
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list graphical processes from terminal

Do no confuse the question here with how to list processes graphically, that is not what I am asking. In the Terminal, how can i see which processes have a GUI? as in things like firefox, vlc, geany,...
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How can a background process know its own PID?

I'm using bash on a RH Linux system. Normally, you can get your own PID with the variable $$. However, if a script runs one of its own functions as a background process - that doesn't work; all ...
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How to check how long a process ran after it finished?

Currently I'm using the following to check how long a process is actually running: ps -eo uid,pid,etime | egrep '^ *MY_ID' | egrep 'PID_OF_PROCESS' And that outputs the following: MY_ID ...
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How to get whole command line from a process?

How can I get the command arguments or the whole command line from a running process using its process name? For example this process: # ps PID USER TIME COMMAND 1452 root 0:00 /sbin/...
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root owned program with setuid bit on

Ping is a a program owned by root with the user id bit set. $ ls -l `which ping` -rwsr-xr-x 1 root root 35752 Nov 4 2011 /bin/ping As I understand it, if a user runs the ping process, then the ...
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When a process will go to 'D' state?

I'm using "Linux hostname 2.6.28-15-generic #49-Ubuntu SMP Tue Aug 18 18:40:08 UTC 2009 i686 GNU/Linux" All the client machines will use Thin-client ,I will use my laptop for working and I will ...
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Is there a way to see if process listening on TCP port receives a message?

According to tcpdump, my server receives the following TCP packet: 12:52:29.603233 00:19:e2:9e:df:f0 00:16:3e:6a:25:3f, ethertype IPv4 (0x0800), length 74: 10.10.10.65.38869 192.168.215.82.22: ...
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How to see complete list of processes in top

When I do 'top', I learn that there are many processes running out of which many are in sleep state. I need to see complete snapshot of all processes at that point. the 'top' is able to show listing ...
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will the same pid be used after getting killed?

I had a file opened using vim editor. It was in a ssh session and since I had been idle for a long time, the session got closed and I had to establish the connection again. I opened the file again ...
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Why are there so few “running” processes?

On all of BSD/Linux/MacOS and Solaris, I made an observation - no matter how busy the system is, top always reports very few (usually 1-2) running processes. According to my limited understanding, a ...
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What does it mean each process has a current directory?

I'm reading "The Unix Programming Environment", but I don't comprehend the concept current directory of process. Each process, has a current directory, and all filenames are implicitly assumed ...
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Find processes using a network interface

I'm trying to find a way to safely shutdown a network interface, i.e. without disturbing any processes. For this I need to find out what processes are currently using that interface. Tools like ss, ...
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How can I chase a program who is rising up my laptop's temperature?

After 40 days of non-upgrading I came back from a trip and I decided to dist-upgrade my Debian Sid box. Everything went fine but after rebooting I noticed that the temperature was 15°C over its ...
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Can I pipe any two processes to each other?

In this page from The Design and Implementation of the 4.4BSD Operating System, it is said that: A major difference between pipes and sockets is that pipes require a common parent process to set ...
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Using `kill -s 0 $pid` vs `[[ -e /proc/$pid ]]` to detect if PID is running

One of the idioms often used to check if process is running is to use kill -s 0 $pid. My question is, does it have any upsides over using [[ -e /proc/$pid ]] construct? The script I'm writing is ...
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How to find Heap memory of a running process? [duplicate]

I would like to know how to find the heap memory of a process that is running in the background. Is there any command that allows such?
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What's the best way to determine the working directory for UNIX process using 'ps'?

I am running a Ruby command line script (rufus.sh)which ultimately calls Thread.new, which spawns a UNIX process as shown below. I run this script for more than 1 directory as the output of the ps ...
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Change the parent process of a process?

Is it possible to change the parent process of a process? If yes, how? For example, how does screen manage to attach a screen session and the processes running inside it to different shell ...
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Monitoring filesystem activity

Say, I have a program, and I want to monitor its filesystem activity (what files/directories are created/modified/deleted etc.) This program may be capable of spawning further processes, and thus, I ...
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Obtaining PID of command earlier in Pipeline

I'm writing a bash script to use inotifywait to monitor a directory and kick off actions when changes are detected. Something like: inotifywait -m ... | while read f; do something; done Since ...
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Bash script wait for processes and get return code

I am trying to create a script which will start many background command. For each background command I need to get the return code. I have been trying the following script : #!/bin/bash set -x pid=(...
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What does '?' represent under TTY

If you run ps in your terminal, you may see something like the following: What is ?? I'm ssh'ing into a Linux server, so I assume that it's just the sshd as it says under CMD, but I'm curious what ...
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Is a persistent zombie process sign of a bug?

(OS: Debian variant.) Having a process with zombie-status. The PPid belonged to a gvim process. The contents of /proc/[pid]/wchan is do_exit, /comm is sh and /cmdline is empty, /status is shown ...