Would anyone be so kind to explain to me the function of dup() in UNIX? As far as I am concerned, it duplicates a file descriptor. Under what circumstances would we need to duplicate a file descriptor in a UNIX environment?
Thank you.
vinchen (3 Replies)
I have met this code:
switch(fork()) {
case 0:
close(1);
dup(p);
close(p);
close(p);
execvp(<whatever>);
perror("Exec failed");
}
Can anyone tell me what this piece of code does?
Thx alot.. (1 Reply)
I'm having difficulty understanding the purposes of using dup/dup2 when involving forks.
for example, if we call fork() once, that is, we are creating a child process. In what cases would we need to use dup or dup2 to duplicate the file descriptors for standard output and standard error? What... (1 Reply)
Hi, I use this function (now modified with elif) for check if a pc is up: check_pc() {
$PING $PC 1 2> /dev/null
if ; then
check_dir #Other function
echo "Begin backup operation for $PC"
echo "$SMBTAR -s $PC -u $USER -p $PASS -x $SHARE$EXCL -t - | gzip -c >... (3 Replies)
when i want to replace standard output with output file
int out;
out = open("out", O_WRONLY)p;
dup2(out,1);
What Shall I do in case of appending??? I am using here O_WRONLY TO WRITE.BUT IF i wanna append, whats the word? (5 Replies)
Hi,
I have a requirement where I have to identify duplicates from a file based on the first 6 chars (It is fixed width file of 12 chars length) and whenever a duplicate row is found, its original and duplicate row's last 2 chars should be updated to all 0's if they are not same. (I mean last 2... (3 Replies)
Hi Gurus,
I need to count the duplicate records in file
file
abc
abc
def
ghi
ghi
jkl
I want to get below result:
abc ,2
abc, 2
def ,1
ghi ,2
ghi, 2
jkl ,1
or
abc ,2
def ,1 (3 Replies)
help with bash script!
im am working on this script to make sure my server will stay online, so i made this script..
HOSTS="192.168.138.155"
COUNT=4
pingtest(){
for myhost in "$@"
do
ping -c "$COUNT" "$myhost" &&return 1
done
return 0
}
if pingtest $HOSTS
#100% failed... (4 Replies)
The problematic directory is the following:
/root/.cache/deja-dup
This directory grows until my "/" is full and then the restoring activity fails.
I already tried to create a symbolic link with origin another partition where I have more space. However during the restoring activity ... (4 Replies)
Discussion started by: puertas12
4 Replies
LEARN ABOUT DEBIAN
arpsend
arpsend(8) Containers arpsend(8)NAME
arpsend - send ARP requests
SYNOPSIS
arpsend -D -e target_ip [ -e target_ip ...] [-c count] [-w timeout] interface
arpsend -U -i source_ip [-c count] [-w timeout] interface
DESCRIPTION
Utility arpsend sends ARP packets on device interface to detect or update neighbours' ARP caches with a given IP.
COMMANDS
Run utility with one of the following commands:
-D Send broadcast ARP request to detect neighbours with target_ip. You have to specify target_ip (-e option).
-U Send broadcast ARP request to update neighbours' ARP caches with source_ip. You have to specify source_ip (-i option).
OPTIONS -c count
Number of packets to send. Default is infinity.
-w interval
Interval between packets, in seconds. Default is 1 second.
-i source_ip_address
Set source IP address field in ARP packet.
-e target_ip_address
Set target IP address field in ARP packet. Note that you can specify -e option multiple times to detect many IP addresses in one
utility call.
EXIT STATUS
arpsend returns 0 upon successful execution. If something goes wrong, it returns an appropriate error code.
1 EXC_USAGE
Usage error
2 EXC_SYSTEM
System error
3 EXC_RECV
ARP reply was received
EXAMPLES
To send request on interface eth0 to detect any neighbour computers with IP 192.168.10.200:
arpsend -D -e 192.168.10.200 eth0
To send request on interface eth0 to update neighbours' ARP caches with IP 192.168.10.200:
arpsend -U -i 192.168.10.200 eth0
NOTES
Interface you use have to be arpable and not be loopback (i.e. /sbin/ip link show interface should show neither NOARP nor LOOPBACK flags
in interface parameters).
SEE ALSO vzctl(8).
LICENSE
Copyright (C) 2000-2011, Parallels, Inc. Licensed under GNU GPL.
OpenVZ 28 Jun 2011 arpsend(8)