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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Dear Experts

In windows server where the application server (CRM system)  is deployed this application which connects to multiple integrations like website , CTI, also configured office 365 smtp, the application logs are not giving us enough data hence from the windows server level how to find or get the log report , when the CRM application runs logic based on scheduler it triggers emails to the customers to check this from windows server level what to do please suggest, in linux think we can use netstat - tulnp, In windows server how to find the application which is running is it establishing connection to the remote services like smtp configured. for example
1.  would like to run the command where it lists  only the running smtp connections established
2. would like to run the command where it lists all the connections established to web server.
also is it possible to append to text file
CompTIA Security+
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CompTIA Security+

Learn the essential functions of CompTIA Security+, which establishes the core knowledge required of any cybersecurity role and leads professionals into intermediate-level cybersecurity jobs.

Dear Wizards, I setup the ubuntu 16.04 server in vSphere 6.5 with 250 GB hard disk, but days later I increased it to 500 GB, but seems like the VM still had only 250 GB.

How can I claim it back correctly? Many thanks!

After 30+ hours of research and trying different solutions I have found many solutions to each piece of this puzzle but can't quite get them to work together or figure out the best approach so I'm hoping you guys can help.

The goal: Use public IP from a remote server(Ubuntu) as a browser proxy. The kicker is that the server should pass all traffic through to a local machine which has a 4g modem internet connection to use its internet connection. We need to be able to assign fixed IP addresses/IP port combinations to these local modem/s to be used as undetectable browser proxies to make it appear that the browser client is logged in using the mobile internet connection.

I have seen multiple solutions to each part of this including the use of ssh tunnels, dynamic port forwarding/socks, remote port forwarding, squid proxy server/other proxy server software, iptables configs etc..

I have found this solution that I can get traffic to travel from anywhere to my local machine:

//1st terminal establishes connection/tunnel ssh -nN -R 8888:localhost:8889 -i "connection.pem"

//2nd terminal listens on port 8889 netcat -l -p 8889 //this command works and prints abc on the local machine echo "abc" | nc -v xx.xx.xx.xx(remote server ip) 8888

I have also successfully installed a squid proxy server in a docker container and used the following command to open socks connection with reverse forwarded port.

//Socks/Dynamic forwarding with…
Does anyone know How can I see the interface up and down logs in the ubuntu 18.4? there should be something like /var/log/dmesg shows logs
how to grep multiple awks

$ awk '{print;}' employee.txt
100  Thomas  Manager    Sales       $5,000
200  Jason   Developer  Technology  $5,500
300  Sanjay  Sysadmin   Technology  $7,000
400  Nisha   Manager    Marketing   $9,500
500  Randy   DBA        Technology  $6,000

$ awk '{print $2,$5;}' employee.txt
Thomas $5,000
Jason $5,500
Sanjay $7,000
Nisha $9,500
Randy $6,000

in above query how to tweak to see  see all records whose name starts with 'S' and Salary greater than '6000'

in above query how to tweak to see  see all records whose name starts with 'S' and Salary greater than '6000' and Department Starts with  'T'

100  Thomas  Manager    Sales       $5,000     08/08/1988 6:00:01AM
200  Jason   Developer  Technology  $5,500 08/08/1989 7:00:02AM
300  Sanjay  Sysadmin   Technology  $7,000 08/08/1982 9:00:03AM
400  Nisha   Manager    Marketing   $9,500 08/08/1981 10:00:04AM
500  Randy   DBA        Technology  $6,000 08/08/1981 11:00:5AM
if it has joined date and time as above
in above query how to tweak to see  see all records whose name starts with 'S' and Salary greater than '6000' and Department Starts with  'T' and joined between particular date time to particular date time say  08/08/1982 9:00:03 AM till 08/08/1981 10:00:04AM
i need to use above in a zgrep command
Dear Experts

We are having web-based application on linux which uses LAMP  which is production server recently the web-based application stops working for some time later it resumes back and when checked the /var/log/messages can find the following
kernel: Out of memory: Kill process 249606 (httpd) score 32 or sacrifice child
Sep 13 13:19:27 NYSWB kernel: Killed process 249606, UID 48, (httpd) total-vm:2826972kB, anon-rss:1334424kB, file-rss:2044kB
attached /cat/proc/meminfo and also fdisk -l , the system has 32G of physical RAM,
please suggest should i have to create one more swap partition OR should I have to edit swap config if yes please help me with steps, or any other steps on any config to be done please let me know, thank you.
Dear Experts

I am running crm system web-based which is LAMP stack the web root is /var/ww/html/crmapp and the CRM system reads the files from windows share that is from 2 windows server and executes the logic as per the process developed but I am getting following error from /var/log/messages , attached /etc/fstab, df -h and nswitch.conf, can you please help me in first windows share mount to the same path of web root is it recommend and also is the fstab entires are correct please suggest as the system is very slow.

automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Sep 11 20:06:15 NYSWB automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Sep 11 20:06:17 NYSWB automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Sep 11 20:06:19 NYSWB automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Sep 11 20:06:21 NYSWB automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Sep 11 20:06:23 NYSWB automount[2560]: problem reading master map, maximum wait exceeded
Sep 11 20:06:23 NYSWB automount[2560]: automount: warning: could not read at least one map source after waiting, continuing ...
Sep 11 20:06:23 NYSWB automount[2560]: syntax error in map near [ * -fstype=autofs,-Dhost=& file: ]
Dear Experts

application server web-based of LAMP stack becomes extremely slow and makes application unable to use, web-server(application file system) is having 16GB Ram and database server is separate with 64GB ram and did run mysql tuner attached for your reference below posted recommendation section, when try to set values as recommended mysql fails to start  withe following error log, please help on what values to set so that below error is fixed, thank youmysqltuner12.txt
Plugin 'InnoDB' init function returned error.
180911 14:18:19 Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
180911 14:18:19 Unknown/unsupported storage engine: InnoDB
180911 14:18:19 Aborting

Below -extract of recommendations section from the attached

-- Recommendations ---------------------------------------------------------------------------
General recommendations:
    Control warning line(s) into /var/log/mysqld.log file
    Control error line(s) into /var/log/mysqld.log file
    Set up a Password for user with the following SQL statement ( SET PASSWORD FOR 'user'@'SpecificDNSorIp' = PASSWORD('secure_password'); )
    Restrict Host for user@% to user@SpecificDNSorIp
    MySQL was started within the last 24 hours - recommendations may be inaccurate
    Reduce your overall MySQL memory footprint for system stability
    Dedicate this server to your database for highest performance.
    Adjust your join queries to always utilize …
Dear Experts
We are having CRM application which is web-based runs on LAMP stack. the operation team reports between specific time period user get time out when they save the records or convert the records or retrieve the records, can you please suggest on how to capture log files which occurs during that time for example 5pm to 6pm, only during this time I would like to capture a following log files.
1) /var/log/mysql.log
3) /var/log/slowquerylog
please help with steps on above 1 to 4 log capture during specific time period , this will be helpful to investigate , thank you very much.
I am sysadmin..I want to know

I want to reach the server, to check the connectivity thru specific port.
This is just to varify whether the required firewall rule defined properly or not.
Learn SQL Server Core 2016
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Learn SQL Server Core 2016

This course will introduce you to SQL Server Core 2016, as well as teach you about SSMS, data tools, installation, server configuration, using Management Studio, and writing and executing queries.

Consider the below scenario

userPC---- firewall --- Destination-server

I have installed some software on the server, the service  of that software is using port # 301.

1) Scenario...
      Firewall defined
      server#  service UP
        userPC# telnet 301  --> user get reply

      Firewall defined
      server# service DOWN

is there any command/3rdparty-tools available to just varify, pockets from userPC able to reach on the server through port#301

This I asked just to segregate if there any issue, problem from firewall side (or) destination server side.
awk query
 unzip -c  xyz.log.20180905.gz| awk '$0>= "2013-Sep-09 18:33" && $0 <="2013-Sep-09 23:15"'| grep '|[1-9][0-9][0-9][0-9][0-9]|0000'|wc -l
Zip file too big (greater than 4294959102 bytes)
  End-of-central-directory signature not found.  Either this file is not
  a zipfile, or it constitutes one disk of a multi-part archive.  In the
  latter case the central directory and zipfile comment will be found on
  the last disk(s) of this archive.
how to learn awk any good video tutorials on it?
please advise
Dear Experts

in linux server of centos,  we are running crm which is web based application apache, mysql and php once in few hours users are getting timeout and this is affecting very badly,
1. would like to fetch the log reports of server resources consumption like  RAM, CPU to understand the issue is occurring due to over load of that particular time.
2.  would like to fetch apache logs and mysql logs of that particular time
to determine the time that users are facing issues of application time out , Can I ask software developer to provide me time out occurred and application closed  date and time and during that time check the server resource utilisation which will help me to trace the issue is it due to server or application level.
please help on best practice on such cases.
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 ?
I have a samba domain controller. all my ubuntu server is on domain. i created a group in ad.
But this group is unknown for all my ubuntu servers.
users can login to server via domain password. and all server answer back for wbinfo -g.
how to active domain groups in ubuntu servers?
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.
Python 3 Fundamentals
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Python 3 Fundamentals

This course will teach participants about installing and configuring Python, syntax, importing, statements, types, strings, booleans, files, lists, tuples, comprehensions, functions, and classes.

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.

I'm running CentOS Linux release 7.4.1708 (Core), issue is i'm able to login using local users but not using ldap users, please help me on this.

I've tried restarting services using authconfig-tui command, but still i'm getting authentication failure error for ldap user.

please see the attached doc (ldap issue.docx), and below output commands and let me know if any other details are required.

[root@server01 log]# cat /etc/openldap/ldap.conf
URI ldap://<ldap servrer ip>:389/
BASE dc=prod,dc=hclpnp,dc=com
[root@server01 log]# getent passwd testuser
[root@server01 log]#

[hubba@servder01 ~]$ su - testuser
su: Authentication failure

[root@server01 log]# cat /etc/nsswitch.conf
# /etc/nsswitch.conf
# An example Name Service Switch config file. This file should be
# sorted with the most-used services at the beginning.
# The entry '[NOTFOUND=return]' means that the search for an
# entry should stop if the search in the previous entry turned
# up nothing. Note that if the search failed due to some other reason
# (like no NIS server responding) then the search continues with the
# next entry.
# Valid entries include:
#       nisplus                 Use NIS+ (NIS version 3)
#       nis                     Use NIS (NIS version 2), also called YP
#       dns                     Use DNS (Domain Name Service)
#       files              …
Hi guys, I'm currently doing send mail to fax by using hylafax. I'm using thunderbird to send mail to my fax machine. The mail address looks like this So my current problem is when i send the mail to the fax machine, what i received at the machine was all the log text, my sent content was not there, it print out the log message in /temp/mail2faxlog
i will attach my postfix,,  and my valias file in here.

My transport file looks like this: fax:localhost

My valias mail2fax

I'm currently following these guide:
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 …

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