Linux Networking





The variety of Linux distributions creates myriad issues relating to configuration and operations when computers are networked, not the least of which is the use of various network management applications, some of which are included with specific distributions, while others are standalone applications.

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zgrep 'XYZ|AB|MASTER' AAAA.log.20180904.gz | grep '|[1-9][0-9][0-9][0-9][0-9]|0000' | wc -l

can you please advise what is the meaning of above zgrep command

where i can find, practice and learn above kind of commands

how grep and egrep are different
how to learn regular expressions used in queries

Please advise
rsync error on ubuntu 16.04 server.
i try to sync folder between two ubuntu server and say
sshpass -p password@ rsync  ssh -avhre user@ip_server:/home/my/direct/ /home/my/
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1655) [generator=3.1.1]

Hi ..CCan anyone tell me what is this service "icl-twobase1" running on port 25000 ?
Hello Experts,
I am trying to change the mail behavior of fail2ban to /etc/fail2ban/jail.local section mta=.
I would like to generate a fail2ban mail filter that uses swaks as mail client although the authentication, mail from, mail to are already pre-set. Unfortunately I don't find any meaningful examples in my internet search and wanted to ask politely if someone has such a configuration already running. Thank you so much

With kind regards reredok
I want to create a server(OS: CentOS) which will be acting as an interface to an Android app(client) and the database.

I am not much experienced in programming and I just want a little bit of guidance right now to get started.
I have decided that I want to program the server in C++(though it's not an easy language but I believe there's much more to learn while programming in C++)

The basic functionality I want from my server:
1. It will interact with the app via https.
2. The server and client(app) will communicate via REST APIs.

I want guidance in terms of the most stable and well documented external C++ libraries that I should use to program the above server(I've looked at zmq, libcurl, netlib-cpp but due to my lack of experience I don't even know if these are really related to my problem statement). Thanks in advance. Please feel free to attach any blog/article/video which might be relevant.
I have multiple NICs on my Redhat 6 x86_64 server and as part of my script I have to determine which NIC is the default gateway on each server since there are lots of static routes over the other NICS. I always see the default gateway as the last line in the routing table but is that logic flawed and I just run net stat -rn | tail -1 | awk '{print $8}' but I'm not sure if that logic is up to par and I'm going to have to tally it up with what's in /etc/sysconfig/network as the gateway.
I recently cleaned my server off, and installed a fresh copy of centos 7 linuxs on it. My issue is i have ssh running, but i am only able to access it with my private ips. I am not clear on how to set it up to use my static ip and domain names? Please help? The domains are not setup yet, since i just installed centos 7 again. i need help with the basic understand of setting my ssh up to allow remote access in another city.  when i try to use my static ip to access it i get this error "port 22: No route to host ". My firewall is complete down, so there or not blocks, so it has to be a configuration issue. i Just dont know what to do to fix it.
Dear All

  I have a centos 7 acting a router, and found out using a speed test the upload speed is very slow, whereas the download speed is reaching 99mbps, I try to by pass the centos and direct connect to a laptop , the upload speed show 99mbps, any idea what limited the upload speed on centos ?

I installed dietpi today on a Zero w. (did it on a 3B+ and setup as Hotspot no problem). I wanted to setup the zero as a webcam.
I did this 4 times before I started to install or change the configuration and reboot at least 2 times to make sure all was good.
I changed the setup to US. connected to the Wi-Fi.
Updated to the latest version of dietpi. Update the firmware.
Changed drop bear to ssh.
installed REALVNC.
But when I Install RPI WEB CAM it keeps rebooting and I can't stop it.
As I said after the 3rd time I flashed a fresh image again and rebooted at least 2 times after each change or install until I got to the RPI Web CAM issue.
I get "You're in emergency mode. Enter root password for maintenance or CTRL D.
I tried dietpi for the password and root. CTRL D does nothing but reboot back to the same area.
I'm assuming there is am issue with RPI Web Cam.
And Yes I made sure the power supply is good. I replaced the power supply with one used on my Pi3B+. It's 5.2V, 3amps.
I even tested it with my voltmeter. The issue is this pi Zero W setup works fine with a full version of Raspian and the RPI WEB CAM version I had to manually configure. I switched back to that card and all is fine. I just like the small footprint and ease of setup with DietPi. And it only starts to reboot when I add in the Web Cam distro on DietPi. I even tried some other packages after my 4th attempt, on the card, flashed a new image. In fact I added a few distros to the DietPi setup …
Dear Experts

in the Windows Active Directory domain controller environment joining the windows client to the domain controller by assigning the IP address and preferred DNS pointing to Windows AD server (which functions as domain controller and also name server).
 Joining the windows client does not require manually creating the entries in the forward and reverse zones, the moment windows client device is joined the records are automatically created in the DNS server.   Now how to make Linux servers in the network to use windows AD server as its  DNS server,  should we have to manually create forward zone and reverse zone entries and then configure Linux server to use windows AD server as its DNS server, please suggest .
file create error on below site

please advise how to create some files and practice grep commands there

any other online free tools to practice unix.

please advise
I have a Proxmox Server.
It has a static ip, setup withbridge  vmbr0.
I can access the internet from it.
However, I cannot do the same

This is my interfaces:
This is my ifconfig:
In my vm instance of CentOS, I changed my static ip with command:
vi /etc/sysconfig/network-scripts/ifcfg-ens18 to include:


I ran command vi /etc/sysconfig/network to include: GATEWAY="" .

I restarted with command: systemctl restart network.service .

I can reach my gateway from the CentOS VM but still can't reach internet.

Still new to this, anyone know what I'm missing?

Now our MySQL cluster test platform do not have internet connection and we need to setup local repository for it.

I check out a lot of googled page and it seems no one exactly match what I am going to install, let see what I go from latest MySQL cluster 7.6.6 binary:

rpm files list.
so for management node, which rpm I should install and what is the command for it? just yum --noplugin localinstall <rpm name> ?

For data node, which rpm I should install?

For SQL  node, which rpm I should install ?
what is the meaning of below command

zgrep 'CUSTOMERPASS' abcd.20180719.gz|grep -v 'Trials: 1'|less

Is there is single link, tutorial or video tutorial where i can find above kind of command
count command


alll commonly used commands like above
why we need | before less?

Please advise
how to find number of count in the unix logs for a grep search keyword say 'nullpointerexception on deviding 109418 with 0' please advise
server times out

i have 15 production unix server instances to check logs same time

when i am on one monitor other monitor times out in every 15 minutes

if i type
tail -f logfile

does it still times out on me

i cannot change time out setting myself

just looking for some work around so that i do not have to enter username and password all over again
transactions search in unix logs

in the unix logs of transactions each transaction has bunch of values like

transaction_id|transaction_time|transaction_description|transaction_type| ......etc

if i want to display only the transactions that took more than say 30 minutes and whose transaction_type is "sell"

how do i frame my grep command for that

any sample queries, links, resources, sample video tutorials on this

Please advise
Dear Experts

I would like to understand the need for Windows Active Directory services OR openldap in the organisation where there are multiple departments and various access controls on network resources like internet access/CRM/ERP, EMAIL.  Each department will have working on different modules of CRM/ERP/network data store. is it recommended to make all the business applications CRM/ERP/email to authenticate with Windows Active Directory services OR openldap,  the organisation has more than 500 users however with branches and each location minimum of 100 to 125 users using the business applications though the internet or mpls connectivity, please help me understand domain controller setup with windows AD/open ldap real benefits for the company wide. thanks.
Hi All,

I'm having an issue with CentOS and webhosting.

wget -O-  works
wget -O- http://myServerIP/    -> 403 Forbidden.

In IIS I would just add the name to the host header.  
How do I configure this or allow the IP to serve the same path as for the IP?

Thanks in advanced.
I have a Red Hat 7.1 server.  I cannot FTP into the RH7.1 server I get a message 530 Login incorrect.
I can receive files if I use FTP from the RH7.1 server but I cannot SEND files from the RH7.1 server.
When attempting to send files from the RH7.1 server a zero length file is put on the receiving server but no data is ever copied to the receiving server and the FTP process on the RH7.1 server hangs.

This is on an internal network with no outside connections so security is not a concern here.
I also tried sftp with no success.

Any suggestions would be greatly appreciated.

Dan Kaib
what is the meaning of below command

less log123.log | grep -i nullpointerexception

why we use less and then grep on it

Please advise
in vi we can use /nullpointerexception to find that string right.

how to find how many occurrence of that string total and go to say 10th occurence line
please advise
when i open with winscp that opens old stale file compared to putty opening of same file say xyz.ccfg

i wonder why winscp does not show recent changs?

please advise
tail -f logfile.log

what is the meaning of above command.

i see logs rolling too fast.

is there is a way i can slow it down to see clearly slowly

any god tips, links, resources on how to debug production logs efficiently just using putty without any fancy costly tools?

please advise
Dear Experts

We are using nextcloud which is on ubuntu 16.04 with php, mysql and apache until now we were using within the local network but now there is a requirement to enable this to external network that is from internet hence would like to procure ssl certificate and install the same,
1.  can you please suggest the good source to purchase the ssl certificates
2. at present users are using this solution  by installing the ssl certificates will it have any impact of not functioning or breaking down the system please suggest.
3. can you please help me how to install the ssl certificate in this server instance

Linux Networking





The variety of Linux distributions creates myriad issues relating to configuration and operations when computers are networked, not the least of which is the use of various network management applications, some of which are included with specific distributions, while others are standalone applications.

Top Experts In
Linux Networking