General :: How To Create Multiple Children Before Any Child Executes
Aug 27, 2010
Iv got an assignment to complete and I'm stuck at the basic level.
A part of the assigned problem is :
The main process will read the file, and will create N number of child processes (Where N is taken as input) as early as possible before all the children starts its execution. Before creation of each child, the main process should read the file to store all the required data in then corresponding data structure. Child processes should not read the file for getting their information.
As far as my knowledge about this , the child executes before the parent. How do I make the parent not pass the control to it's children before it finishes creating all the children?
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Dec 6, 2010
I am trying to create a script that creates a vector and displays it. I used the command inivec but it didn't work.
[code]...
How do I make it so the terminal executes mi script to create a vector. I know MV is the name and the output should be aa aa aa, but nothing?
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Apr 4, 2011
I'm writing a bash script that executes a few perl scripts. One of the perl scripts that I need to execute requires two arguments with it. The arguments are stored in a txt file, each line contains a hostname and its corresponding IP address separated by a ":" (colon), the txt file looks like this below:
[Code]...
I'm not sure if it's the best way to accomplish this but here it goes. In the bash file, let's call it getHosts.sh, I create an array and assign each line of the file to an element in that array. I then think I need to create a new array where I take the hostname (which is before the ":") separate it from its IP address and place the IP address on a new line just below the hostname (this way I can reference to it like $hostNames[$x] would be the hostname, and $hostNames[$x+1] would be its IP address). So the new array would now look like this below:
[Code]...
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Apr 21, 2010
Recently I have renovated an old computer which once belonged to my dad (the old HDD crashed, and I just bought a new one to replace it). My parents want me to fix this computer for my 5-year-old sister to use. I decided to use Linux Mint as the OS because everything (flash, mp3, etc.) is already configured.
How do I create a user account in Linux Mint with limited access for my sister, so that it won't mess up the entire system?
All she does is surf the web, so I'm just worried that she might accidentally mess up a system setting that I eventually will have to fix it.
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Jul 30, 2009
I am troubleshooting something and I got this problem.
If I do "pstree -p"
It shows,
Code:
[code]....
However, it does NOT show up in "ps -elf"
Code:
ps -elf | grep soffi
0 S whho 7734 1 0 80 0 - 36435 - 11:14 pts/2 00:00:03 /usr/lib/openoffice/program/soffice.bin -splash-pipe=5
0 S whho 7833 7759 0 80 0 - 751 - 11:21 pts/3 00:00:00 grep soffi
I was wondering if 7735, 7736, 7737, 7743 were really processes. Then I checked /proc, I could cd to /proc/7735, /proc/7736, etc, but I could not ls them out. I looked at the man page of "pstree", it says,
Code:
Child threads of a process are found under the parent process and are shown with the process name in curly braces, e.g.
icecast2---13*[{icecast2}]
So, what does all this mean? Does it mean that 7735, 7736, 7737, 7743 are just threads but not processes? If so, why could I cd to /proc/<id> but not see them in "ps -elf".
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Oct 26, 2010
I'm trying to connect one computer to two others in an ad-hoc infrastructure.
[computer 1] ---- [computer 2] ---- [computer 3]
computer 2 is running Linux and has a single NIC wlan0. I want to it to connect to both computer 1 and computer 3 so each computer can talk to the other. No switch is available so it needs to be an ad-hoc setup.
[Code]...
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Jan 5, 2011
I am trying to create a RS232 C program that executes a series of commands down the line to a robot. Everything seems to work fine, except any sequential write to the serial port. At first I thought it was the UART's buffer being filled too fast, but even with a 50 uS delay it still throws the error.
Here is my code:
Code:
#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>
[Code]...
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May 20, 2011
What I need is, given a process id, list all his children without any clutter (table header, other columns than the pid) What I have is :
ps h --ppid $PID Which gives me:
26277 pts/13 S+ 0:10 cmd1
26280 pts/13 S+ 0:10 cmd2
Using h allow me to hide the table header. Is there a way to tell ps to not print the pts/13 S+ 0:10 cmd part in order to get a list of children process ids separated by carriage return?
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Sep 3, 2010
I'm looking for a way in Perl to be able to take a list of servers, ssh multiple commands to it and store the results. If I do this process serially, sometimes one server will hang the whole script and if it doesn't, it still takes hours to complete.
I'm thinking what I need to do is make a parent loop that calls out a separate process that passes the server name to the child sub process and then executes all the commands I have defined in its own process. If one server 'hangs', at least that won't stop the script from doing all the other servers in the list.
I'm guessing using the fork() command would serve me best, however, all the online descriptions I have found have been vague at best.
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Aug 14, 2009
I'm trying to create a CentOS based liveCD that mounts a NFS share and executes one script there. The NFS never mounts altough while logged I can mount it with the very same command that I use in the KS.
In the %post I have :
%post --log=/tmp/post.log --erroronfail
mkdir /mnt/nfs
mount -o nolock 10.23.1.1:/csc/RemoteHome /mnt/nfs
I added the --log in order to debug, but nothing is written in /tmp/post.log. I tried redirection on the mount command with >> /tmp/debug.log but this is not written. Maybe during the post sequence /tmp is RO ? Anyway, I tried with ifup lo, service portmap start in the %post, but doesnt change (I even have a service : command not found in the live cd creator output).
Here is the remainder of the KS :
lang en_US.UTF-8
keyboard us
timezone US/Eastern
[Code]...
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May 21, 2011
what i'm trying to do is create some distance between sets of child nodes in my freemind maps. See the attached png file to see what im getting at. Is there a way to do this, other than using clouds?
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May 23, 2011
I have a doubt about signals in C programming. I have done this little program to explain it. It creates a child process with fork and, when the child ends, receives the SIGCHLD signal and wait for its termination.Ok, quite easy, BUT when I execute this code the SIGCHLD signal is received twice, first as an error (returns -1) and the second one to finish the child process.I don't understand the meaning of the first received signal. Why is it generated? Is the code wrong? (if you add the SIGINT and press Ctrl+C during the execution it also receives two signals instead of one)
Code: #include <stdio.h>
#include <unistd.h>
#include <string.h>
[code]....
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Aug 3, 2011
How do I divide my hard drive into multiple OS'es/partitions for my test machine? For example:
Win XP
Win 7
Gentoo
Ubuntu
Storage
Can Linux'es share swap area? I was told to leave the first primary for the grub and linux cores.
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Apr 24, 2010
I have an unencrypted DVD that is one big title, ie you cannot skip next / prev. What I want to do is reauthor the DVD with title at certain points, so that I can skip next / prev when watching it.
I'm using Ubuntu 8.10
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Feb 18, 2010
I have 5 files in directory /test1
I want to make symbolic links for all them to my current directory /test2
I tried
But it failed. It seems like I can't make symbolic links for all the 5 files simultaneously.
Often times I need make symbolic links for multiple files with some common pattern (just like ".txt" here). I really hope to avoid making symbolic link for each of them one by one...
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May 26, 2010
First post from a very new Linux user....I am trying to create a BASH script that will allow user to provide multiple directory names, Checks if the directory exists and if not create the directory.
I am using the following code:
Which works fine as long as the user enters a single directory name. How can I modify this so it will process all directory names user enters on the read response?
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Nov 20, 2010
My partition layout is as follows:
sda1: 14GB / ext4
sda2: 10GB /iso ext4
sda3: 4GB /home ext4
sda4: 86GB Extended
sad5: 2GB swap
I have 84GB free space on this hard drive and want to install another distro. Will I be able to create another / and /home partitions for the new distro?
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Jul 28, 2011
I have a hard to reproduce (seen a couple times in a month) issue where my program seems like it is hung (not increasing in cputime), however, it is in the runnable state and never gets to run. The cpus are 99% idle according to vmstat and the load is 5 (which is equal to the number of threads in my program that are in the R state) according to ps, and there are no processes on the system in the 'D' state. The other major oddity is that one of the migration threads has a cputime usage almost equal to the uptime of the system. Typically migration threads have a cputime on the order of seconds across hundreds of days of uptime, but in this case the migration thread has DAYS of cputime according to ps.
The last time this happened, I went around saving as much /proc/X information that I could into logs for referring to later, before I had to reboot the box to get it running back to normal. (because in this state, a kill -9 is not heeded by my program)Does anyone have any idea what could cause this? I am not sure if this is a scheduling bug or a bug in my program (the likelier case).I have a wealth of logs to look through if anyone can suggest something specific to look for.
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Apr 8, 2010
I am creating a new user for my son, but I don't want him to have access to M15+ games that are installed (eg Freedoom). Is there a way to deny a user's access to individual programs (or groups of programs). Also for the moment, I would really want him to only have access to a folder with his name on it and not to all of my drives and files on them. Is this possible? I couldn't find it anywhere...
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Feb 3, 2010
I need to create a single line of output from multiple and variable lines of input in a Linux bash shell script.
My input file looks like this:
Where there may be any number of umsecondaryphonenumber lines; if there is not a umsecondaryphonenumber line for a telephonenumber, I don't want to write any output.
So, the output file should look like:
The script I have so far is:
My question is - how do print each of the elements of an array in one record - i.e. what do I put in place of howdoiprintarray?
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Sep 16, 2009
Being new to this area .I have been assigned a task which i am unable to do . Can any one please help me .
I have requirement where i have input file XYZ_111_999_YYYYMMDD_1.TXT and with header and series of Numbers and Footer.
I want to create a mutiple output files with each file having a seperate code which is stored in text file and create XYZ_222_999_YYYYMMDD_1.TXT . and add date in the contents next to series of numbers .Like this
Before change the file looks like this
file name XYZ_111_999_YYYYMMDD_1.TXT
001,19SEP2009-14:05:05,000000003
1234
4567
6785
END_OF_DATA
[Code]....
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Jan 8, 2011
I have a logfile which looks like:
tableabc 1786rows
tabledfg 8374rows
tablefhd 726rows
[code].......
Now i have to writ a script which takes this log as input and quesries the DB for each table. So,I want to: input the logfile
start a while loop.So,while read LINE This variable LINE would store the table name by CUT using a delimiter once the table name is ready it makes a connection to DB and queries the table for its rowcount writes the rowcount to an O/P file.
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Jan 5, 2011
I am trying to write a script that connects to a server and executes some commands on there. Something like this:
#!/bin/sh
telnet remote_machine
cd /home/some_directory
cat a_file_in_current_directory
Unfortunately after login/password I guess the script doesn't jump past the telnet command, until I exit. What do I need to do to make the script start executing commands in the remote shell?
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Aug 27, 2010
I am currently programming a suite of daemons in c++ on CentOS 64. More or less all those daemons are SOAP servers, with the SOAP part handled by gSOAP.
One of the daemons is a monitor sitting on a certain server and more or less just checking if the other daemons are up and running - but also offering a SOAP interface to get the 'current situation' on the machine.
Whenever the detected situation does not correspond to the defined (i.E. a process which should be is not running) it is started up.
This part, I implemented via a system() call that starts the other process.
I was a little confused when lately often this monitoring process would not start because it could not bind its server port - the one the SOAP server is listening on.
And confusion got bigger when netstat told me that the port is assigned to one of the processes that were before started by the monitor..?
Even better: if I then kill the process of which netstat tells me it holds the port, the next netstat shows the next monitor-started process as the one listening on the port..
Only if I kill all the processes that were started by the monitor, the port is released and I am able to launch the monitor again.
Now I wonder: why does this port get 'reassigned' to the children - and most of all: how can I prevent this from happening?
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Dec 7, 2009
Consider the following code:
Code:
int main()
{
int i=0;
pid_t pid;
for(i=0;i<2;i++)
[code]....
I get the following output:
Parent: chid_pid=4356 i=0 parent's pid=4355
This is child 4356 i=0
This is child 4357 i=1
[code]....
I can observe instead of two children(as I expect) processes there are three. This is because child process 4356 creates its own child. Why all the messages of the type "This is child X i=Y" are concentrated one under another? How exactly fork works? Is affected by the fact that I have a dual-core processor?
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May 15, 2011
I want to make a webserver with multiple users allowed to login through SFTP to a specific folder, www.Multiple users are added, lets say user1 and user2, and all of them belonging to the www-data group. The www directory has an owner www-data and a group www-data.
I have used chmod -R 775 on the www folder, but after I try to create a folder test through my SFTP server (using Filezilla) the group of the directory created has only r and x permissions, and I am not able to log in with the second user user2 and create a directory within www/test due to a lack of w permission to the group.
I also tried using chmod 2775 on www directory, but without luck. Can somebody explain to me, how can I make it so that a newly created directory inherits the root directory group permissions?
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Feb 15, 2011
I'm trying to write a script that uses the 'du' command to make essentially a text-based filelight type program. It should scan the current directory for the file's sizes and display them in order largest to smallest (or vice versa). The user should be able to go throughout the file tree and see child directories scanned for the sizes as they're accessed. I just need to know one more thing- how can I restrict the displayed results to the current working directory? would a grep for the output of pwd suffice? just getting some thoughts before i try and possibly dig myself a hole.
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Feb 4, 2010
I have following script.
Code:
#!/bin/bash
export VAR="shell"
echo " $VAR in parent "
bash
echo "shell in child "
If i execute this script, the output is just
Code:
shell in parent
Why can't I see the output shell in child ?
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Dec 17, 2010
What happens to a child process that dies and has no parent process to wait for it and what's bad about this?
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Jul 27, 2011
In my program, I fork() to get a child process. Because of some problem, child process terminates by a segmentation fault. Parent process is still running. I have compiled my code with -g option. I have done: ulimit -c unlimited. I am not getting core dump of the child process. How can I get the core dump of child process?
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