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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Hello Experts,

I have a DELL server that I am going to mirror a couple of hard drives. It needs to become a file server.

My question is, is there a NAS software I could install on it and make it NAS server?

Software like FreeNAS or OpenFile. I will like the software to be free or otherwise, I will use a Linux server like CentOS 7 or Ubuntu.

If that is the case configuring Samba will be enough? Recommendation needed, please.

Thank you!
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Hello everyone!. Perhaps somebody could help me. I am trying to configure firewallD (Centos 7) so public network only has access to http and https services but my trusted networks to ssh, webmin, http, https, etc...
Btw I have only 1 interface.

I need to achieve something like this:

-interface: eth0
-allowed services: http, https

-interface: eth0
-allowed services: http, https, ssh
-allowed ports: 10000

Ho can I do it?
Dear Experts

We are in process of setting up very small IT infra where local dns (private dns server) be done on ubuntu server16.4.4.  We will be hosting web based application server in on-premise and for the internet we have 2 service providers  both are of different,
1.  ISP 1 provided device enabled with the dhcp service for the network and it is ON with the subnet of  this is more stable connection
2. ISP2 also provided device and enabled with DHCP service for the network and they are asking to turn it ON -
purpose of 2 service provider is to have backup when one is down operation can happen with other service provider
As of now I have not yet turned ISP-2 modem/router ON as this will also function as DHCP server and in a network 2 DHCP server cannot be enabled.
Please suggest the best practice
1. Should I have to ask ISP-2 to configure for different subnet like and configure one DHCP server in linux server define 2 subnets here and stop both service providers ISP-1 and ISP-2 modem/router DHCP service but when the clients systems boot which subnet to be released as ISP-1 may be down and but the DHCP server release the IP of subnet ISP-1 , how to switch here to another subnet - NOT sure if this is good way to go with please suggest
2. stop dhcp service of ISP-1 and ISP-2 devices and configure dhcp server in linux but with one subnet only but segment the ip range for ISP-1  router and gateway sections pointing to ISP-1 in dhcp …
Would anyone know if there is an open source firmware like WRT or Tomato that will work in a Netgear FVS318N? I have a number of these and would like to use OpenVPN but am limited by the Netgear firmware among other limitations. It would be great to have the robustness of WRT or Tomato on one of these.
Any thoughts?

I am seeing a lot of collisions and errors on a WAN port (Sophos SG210) which connects to fiber NTU ( Cisco ME 3400E)

This is 100Mb up/down fiber but I am getting around 60Mb download and 3Mb upload. I think the cause of the slow upload speed is because of the packet collisions and errors.

I get around 70Mb/70Mb when I connect my laptop directly to the NTP.

What would be the cause of the problem?

Here is ifconfig on the WAN link on SG210.

eth1   Link encap:Ethernet HWaddr xx:xx:xx:xx:xx:xx
          inet Mask:
          RX packets:373271 errors:0 dropped:0 overruns:0 frame:0
          TX packets:220080 errors:2306 dropped:0 overruns:0 carrier:2306
          collisions:128842 txqueuelen:1000
          RX bytes:527821557 (503.3 Mb) TX bytes:48346583 (46.1 Mb)

 ethtool eth1
Settings for eth1:
        Supported ports: [ TP ]
        Supported link modes: 10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Advertised link modes: 10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
If you have two accounts in AWS with one linux host in each - what options do you have to copy files (sftp) between the two hosts?
What would be the options? What would be the fastest? The least costly?
General concept of openVPN solution for private network. I'm thinking about layer2 bridging mode but... I have one VPS server with Ubuntu 16.04LTS, one local network and two mobile pcs. Starting from server - there is one Ethernet controller with public static IP address. I want to connect to them from 3 places. Should I create 3 TAP interfaces? What about the bridge - bridging eth with TAP(s) or only TAPs from network for example Next computer is PC in local network also with one Ethernet controller with address from network and Gateway Additionaly two laptops with two network cards, one used for internet access with local address from network Have I config TAP and bridge with network card unused or used to connect to internet (WLAN + home WiFi router). I would like to see every computer like in local network, use configured in local network DHCP, DNS (not obliogatory - can be static), used sharing folders, printers, active directory, connect to domain, use DFS. When I trying TUN IP packet routing i probably had wrong configuration but forcing DNS from VPN was disconnecting me from DFS service.
Any help please - routing or bridging and config of TUN/TAPs interfaces with ethernets and Bridges.

Thank You

Hi Team,

I need an help , I have RHEL 6.5 installed on my machine . Its a dual boot. Iam unable to connect to the network.
When I type ifconfig I get two entries
lo Link encap:local loopback
inet addr: Mask:
inet6 addr: ::1/128 Scope:Host

virbr0 Link encap:Ethernet Haddr 52:54:00:4C:9B:91
inet addr: Bcast: Mask:

How can I map the virbr0 to etho  and connect to the network
anyone get vncviewer connecting to an ubuntu 16.04 instance?
i have remote connections enabled but vncviewer (6.17.1113) on windows 10 keeps saying it can't connect with the chosen security setting and to either upgrade vnc server or select weaker encryption.
I already did gsettings set org.gnome.Vino require-encryption false but made no difference
tried every encryption setting in the vnc connection
open ldap on ubuntu server 16.04
i try to install and configure openldap on ubuntu.
i install slapd ldap-utils and i try to start slapd services.
i get error :

slapd.service - LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol)
   Loaded: loaded (/etc/init.d/slapd; bad; vendor preset: enabled)
   Active: failed (Result: exit-code) since 19s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 11693 ExecStart=/etc/init.d/slapd start (code=exited, status=1/FAILURE)

 'ubuntu'systemd[1]: Starting LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol)...
 ubuntu slapd[11693]:  * Starting OpenLDAP slapd
ubuntu slapd[11700]: @(#) $OpenLDAP: slapd  (Ubuntu) (May 30 2017 19:20:53) $
ubuntu slapd[11700]: daemon: bind(9) failed errno=98 (Address already in use)
ubuntu slapd[11693]:!
ubuntu systemd[1]: slapd.service: Control process exited, code=exited status=1
ubuntu systemd[1]: Failed to start LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol).
ubuntu systemd[1]: slapd.service: Unit entered failed state.
ubuntu systemd[1]: slapd.service: Failed with result 'exit-code'.
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Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

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tail -n5000 xyz.log

above shows last 5000 lines right

if i want to see all the 15723 lines of xyz.log what command i have to give

tail -n5000 xyz.log|grep 'ERROR WS'
how to make above case sensitive search like
tail -n5000 xyz.log|grep 'error ws'
how to make above whole word search? so that i wont see below as result ERROR aaa WS etc

please advise

after i installed nextcloud 13.0.1 on centos 7 and most of the features works

i am facing a strange issue with calendar

i cannot create or delete or do anything with calendar on nextcloud management    please check the attached file

do you think i have to change something from GUI or CLI  or install or do something

kindly advice
winscp how to grep or search on a word say "xyz" in all the folders and sub folders
Please advise
Hello Experts,

Getting following error while execute cmd from ssh :-

[root@200 ~]# separateBod
Option "-t" is deprecated and might be removed in a later version of gnome-terminal.
Option "-t" is deprecated and might be removed in a later version of gnome-terminal.
Failed to parse arguments: Cannot open display:

separateBod Code:-
 read IPNAME
 for i in $IPNAME
  ssh user@192.168.1.$i BOD & pid=$!

BOD Code:-
gnome-terminal \
        --tab -t "Exchange" -e " sh -c 'sleep 1s; ./startapp Exchange' "\
        --tab -t "Dragon" -e " sh -c 'sleep 10s; ./startapp Dragon' "\

startapp code:-
ulimit -c unlimited
./$1 $2 $3 $4 $5

After giving execution cmd from server (ssh) it should be displayed on other server vnc (user@, it was working properly till last week suddenly i got this error, we have following versions of CentOS 64bit (6.7, 6.8, 6.9, 7.4), getting issue only with 7.4 64bit.

please suggest.
winscp how to name the link i save to favorite

say i have link

i want to save above link with name as production_logs_folder

I have other link as below


i want to save above link with name as crm_logs_folder

how do i name like above so that it is easy to locate and navigate later
\please advise
log file how to copy whole content

zgrep -C20 '1234' 1234.log.gz

above gave lot of results in unix screen

how to copy whole page and paste into a text file on my C drive of the windows laptop through which i am connecting to unix box using putty?


i see all results like



which i do not want

i want complete word search of 1234 only
how to achieve it
please advise
what is curl and ping in unix.

lets say i have service called

now if do
get the exact_name of service from above result
then use that exact name to ping
ping exact_name
then we can get ip of the service where it is running?

please advise
I can see all processes in my box using memory total as 25GB but the actual memory used is 62GB, I am really confused that what happened for remaining memory....don't know whether i need to clear memory cache or not?

test@test[~] $  ps aux  | awk '{print $6/1024/1024 " GB\t\t" $11}'  | sort -nr | awk '{print $1}' | awk '{total = total + $1}END{print total " GB"}'
24.4622 GB
test@test[~] $ free -g
                            total       used       free     shared    buffers     cached
Mem:                      62         62          0          0               2             32
-/+ buffers/cache:              27         35
Swap:                        7          0          7
test@test[~] $

Open in new window

memory issue
I'm having issues installing auditd on Ubuntu 16.04.  Below is what I get.. Any ideas?

After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up auditd (1:2.4.5-1ubuntu2.1) ...
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Job for auditd.service failed because the control process exited with error code. See "systemctl status auditd.service" and "journalctl -xe" for details.
invoke-rc.d: initscript auditd, action "start" failed.
● auditd.service - Security Auditing Service
   Loaded: loaded (/lib/systemd/system/auditd.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2018-03-07 16:24:26 UTC; 5ms ago
  Process: 3196 ExecStartPost=/sbin/auditctl -R /etc/audit/audit.rules (code=exited, status=0/SUCCESS)
  Process: 3195 ExecStart=/sbin/auditd -n (code=exited, status=1/FAILURE)
 Main PID: 3195 (code=exited, status=1/FAILURE)

Mar 07 16:24:26 support systemd[1]: Starting Security Auditing Service...
Mar 07 16:24:26 support systemd[1]: auditd.service: Main process exited, code=exited, status=1/FAILURE
Mar 07 16:24:26 support systemd[1]: Failed to start Security Auditing Service.
Mar 07 16:24:26 support systemd[1]: auditd.service: Unit entered failed state.
Mar 07 16:24:26 support systemd[1]: auditd.service: Failed with result 'exit-code'.
dpkg: error processing package auditd (--configure):
 subprocess installed …
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i have nagios core version 4.3  installeret på server ubuntu 16.04 . and nrpe version 3 og plugin 2.2.1 from client. on ununtu 16 and 14.
alle works . except for one ubuntu 16.04 i have error connection reset by peer )from nagios server)
from client when i say
./check_nrpe -H ipadress        then connection reset by peer
./check_nrpe -H       working  NRPE 3.2.1
./check_nrpe -H localhost    connect to address ::1 port 5666: Connection refused
NRPE v3.2.1

i have disabled = no on /etc/xie../nrpe
and  only_from       = client-ip  server-ip

from /usr/local/.../nrpe.cfg
allowed_host =,::1,client-ip,server-ip

like all other 16.04 and 14.04.
what is wrong?
how to check production logs

i logged to production server i went to server log path.
i did
ls -ltr

i see bunch of log files at different timestamps

lets say xyz.log is at 1:30 am which i am interested to see.

how to open and hjow to see it?

when i logged using winscp says log in denied to copy over to windows laptoip to check.
like i want to zgprep or grep all "NullPointerErrors" between 12:30 AM till 2:30AM how do i check?
Also how to check how many times it was restarted?
any good best practices on production logs?
please advise any god links, resources on it?
grepping a xyz.tar.gz file?

how to grep a xyz.tar.gz file on unix box?

i moved it to loical using winscp.

how to extract it to see file contents

i used qizip and 7 zip they simply changing zip to tar and then tar to zip again and again

please advise
Hello Experts,

I am working on a Proxmox two server cluster.

I am going to put two server as one cluster to have hardware redundancy. I have read that it is recommended to use 3 servers. We only have two for now.

What technical notes or recommendations will I need to get this project started.
i have install postfix on ubuntu 16.04 for send-only mail.
when i send mail nothing happend nor error and  don't send mail.
service status on postfix  is
fatal: bad numerical configuration: mailbox_size_limit = 20M
fatal: bad numerical configuration: mailbox_size_limit = 20M
warning: process /usr/lib/postfix/sbin/local pid 12388 exit status 1
warning: /usr/lib/postfix/sbin/local: bad command startup -- throttling

what is wrong here what should linit be?
Hi to all of you,
I'm preparing new files Audit rules in the /etc/audit/audit.rules file.
The syntax I'm using is: auditctl -w path_to_file -p permissions -k key_name
example -w /etc/libaudit.conf -p wa -k wlib.conf

My question is: if I use the following syntax without specifing the permission option (-p)
auditctl -w path_to_file -k key_name what is the default permission value used?

Sounds a strange question but this is what I've been asked.
Bye  and thanks

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