I want to use nc as a simple TCP/IP server. So far I run it using:
$ nc -k -l 3000 > temp.tmp
This works, but writes all the received data of all connections into one single file. But, I would like to have individual files.
Basically I get this if I skip the -k switch, but then nc shuts down as soon as the first connection is gone.
How can I keep nc running, but use an individual file for each incoming request? (Or, if this is not possible, is there an alternative *nix tool that is able to do this?)
Please note that I do not want to restart nc, but I want it all with a single running instance.
PS: I know that SO doesn't allow questions on finding tools, but for me this is only the fallback in case nc isn't able to do that by itself. So, sorry for the part in parentheses…
On the receiver:
$ nc -p 3000 -l | tar -x
On the sender:
$ tar -c * | nc <ip_address> 3000
Omit the -k and run it in a loop:
n=0
while nc -l 3000 > "$n".txt ; do
n=$((n+1))
done
I think Cronolog can help in this case
-p option you can determine the period option
Also the filewatcher utility "incron" can be used which will check logs to one file & can split to some other files
Related
I need to ssh into memcached servers and execute ensure connectivity.
I am supposed to re-use the same ssh connection and keep executing the commands whose output will be stored in some log. This is supposed to be a scheduled job which runs at some specific intervals.
Code 1 makes multiple ssh connections for each execution.
#!/bin/bash
USERNAME=ec2-user
HOSTS="10.243.107.xx 10.243.124.xx"
KEY=/home/xxx/xxx.pem
SCRIPT="echo stats | nc localhost 11211 | grep cmd_flush"
for HOSTNAME in ${HOSTS} ; do
ssh -l ${USERNAME} -i ${KEY} ${HOSTNAME} "${SCRIPT}"
done
Code 2 hangs after ssh.
#!/bin/bash
USERNAME=ec2-user
KEY=/home/xxx/xxx.pem
ssh -l ${USERNAME} -i ${KEY} 10.243.xx.xx
while:
do
echo stats | nc localhost 11211 | grep cmd_flush
sleep 1
done
Is there any better way of doing this?
Since you want to have Code 2 run the infinite while loop on the remote host, you can pass that whole thing to the ssh command, after fixing the while statement:
#!/bin/bash
USERNAME=ec2-user
KEY=/home/xxx/xxx.pem
ssh -l ${USERNAME} -i ${KEY} 10.243.xx.xx '
while true
do
echo stats | nc localhost 11211 | grep cmd_flush
sleep 1
done
'
I have to warn that I think the whole approach is somewhat fragile, though. Long-standing ssh connections tend to die for various reasons, which don't always mean the connectivity is actually broken. Make sure the parent script that calls this notices dropped ssh connections and tries again. I guess you can put this script in a loop, and maybe log a warning each time the connection is dropped, and log an error if the connection cannot be re-established.
I am writing a shell script where i want to ssh to a server and get the cpu and memory details data of that displayed as a result. I’m using the help of top command here.
Script line:
ssh -q user#host -n “cd; top -n 1 | egrep ‘Cpu|Mem|Swap’”
But the result is
TERM environment variable is not set.
I had checked the same in the server by entering set | grep TERM and got result as TERM=xterm
Please someone help me on this. Many thanks.
Try using the top -b flag:
ssh -q user#host -n "cd; top -bn 1 | egrep 'Cpu|Mem|Swap'"
This tells top to run non-interactively, and is intended for this sort of use.
top need an environment. You have to add the parameter -t to get the result:
ssh -t user#host -n "top -n 1 | egrep 'Cpu|Mem|Swap'"
Got it..!! Need to make a small modification for the below script line.
ssh -t user#host -n "top -n 1 | egrep 'Cpu|Mem|Swap'"
Instead of -t we need to give -tt. It worked for me.
To execute command top after ssh’ing. It requires a tty to run. Using -tt it will enable a force pseudo-tty allocation.
Thanks stony for providing me a close enough answer!! :)
I have very little experience with Bash but here is what I am trying to accomplish.
I have two different text files with a bunch of server names in them. Before installing any windows updates and rebooting them, I need to disable all the nagios host/service alerts.
host=/Users/bob/WSUS/wsus_test.txt
password="my_password"
while read -r host
do
curl -vs -o /dev/null -d "cmd_mod=2&cmd_typ=25&host=$host&btnSubmit=Commit" "https://nagios.fqdn.here/nagios/cgi-bin/cmd.cgi" -u "bob:$password" -k
done < wsus_test.txt >> /Users/bob/WSUS/diable_test.log 2>&1
This is a reduced form of my current code which works as intended, however, we have servers in a bunch of regions. Each server name is prepended with a 3 letter code based on region (ie, LAX, NYC, etc). Secondly, we have a nagios server in each region so I need the code above to be connecting to the correct regional nagios server based on the server name being passed in.
I tried adding 4 test servers into a text file and just adding a line like this:
if grep lax1 /Users/bob/WSUS/wsus_text.txt; then
<same command as above but with the regional nagios server name>
fi
This doesn't work as intended and nothing is actually disabled/enabled via API calls. Again, I've done very little with Bash so any pointers would be appreciated.
Extract the region from host name and use it in the Nagios URL, like this:
while read -r host; do
region=$(cut -f1 -d- <<< "$host")
curl -vs -o /dev/null -d "cmd_mod=2&cmd_typ=25&host=$host&btnSubmit=Commit" "https://nagios-$region.fqdn.here/nagios/cgi-bin/cmd.cgi" -u "bob:$password" -k
done < wsus_test.txt >> /Users/bob/WSUS/diable_test.log 2>&1
I'm not quite sure what the issue is. I'm on Kali Linux 2.0 right now, fresh install. The following worked on Ubuntu 14.04 but it's not working anymore (maybe I accidentally changed it?). It looks correct to me, but every time it runs it blocks.
backup_folder=$(ssh -i /home/dexter/.ssh/id_rsa $server 'ls -t '$dir' | head -1')
This is part of a larger script. $server and $dir are set. When I run the command alone, I get the correct output, but it doesn't end the connection.
I don't know if this may help to solve the question but your command doesn't handle dirs with space in the filename. Add double quotes inside the single quote section like this:
SERVER='remoteServer' && REMOTE_DIR='remoteDir' && backup_folder=$(ssh -i /home/dexter/.ssh/id_rsa "${SERVER}" 'ls -t "'${REMOTE_DIR}'" | head -n1'); echo "${backup_folder}"
If it doesn't help try to add increasing number of -v switch to ssh to debug eventually reaching:
SERVER='remoteServer' && REMOTE_DIR='remoteDir' && backup_folder=$(ssh -vvv -i /home/dexter/.ssh/id_rsa "${SERVER}" 'ls -t "'${REMOTE_DIR}'" | head -n1'); echo "${backup_folder}"
If the verbose output does not help may be an MTU problem (these kind of problems are not of binary type, acts strangely).
You can try lowering MTU (usually 1500) on your side to solve:
sudo ifconfig eth0 mtu 1048 up
eth0 is obviously an example interface, use your own.
How to write a echo server bash script using tools like nc, echo, xargs, etc capable of simultaneously processing requests from multiple clients each with durable connection?
The best that I've came up so far is
nc -l -p 2000 -c 'xargs -n1 echo'
but it only allows a single connection.
If you use ncat instead of nc your command line works fine with multiple connections but (as you pointed out) without -p.
ncat -l 2000 -k -c 'xargs -n1 echo'
ncat is available at http://nmap.org/ncat/.
P.S. with the original the Hobbit's netcat (nc) the -c flag is not supported.
Update: -k (--keep-open) is now required to handle multiple connections.
Here are some examples. ncat simple services
TCP echo server
ncat -l 2000 --keep-open --exec "/bin/cat"
UDP echo server
ncat -l 2000 --keep-open --udp --exec "/bin/cat"
In case ncat is not an option, socat will also work:
socat TCP4-LISTEN:2000,fork EXEC:cat
The fork is necessary so multiple connections can be accepted. Adding reuseaddr to TCP4-LISTEN may be convenient.
netcat solution pre-installed in Ubunutu
The netcat pre-installed in Ubuntu 16.04 comes from netcat-openbsd, and has no -c option, but the manual gives a solution:
sudo mknod -m 777 fifo p
cat fifo | netcat -l -k localhost 8000 > fifo
Then client example:
echo abc | netcat localhost 8000
TODO: how to modify the input string value? The following does not return any reply:
cat fifo | tr 'a' 'b' | netcat -l -k localhost 8000 > fifo
The remote shell example however works:
cat fifo | /bin/sh -i 2>&1 | netcat -l -k localhost 8000 > fifo
I don't know how to deal with concurrent requests simply however.
what about...
#! /bin/sh
while :; do
/bin/nc.traditional -k -l -p 3342 -c 'xargs -n1 echo'
done