How to resolves zmconfigd service can't start on ZIMBAR 8.5
If you install zimbra 8.5.0 on Centos 7 or Red Hat Enterprise 7 and zmconfigd fails to start, as in this example: [zimbra@ezymailhosting ~]$ zmcontrol status Host mail.amarz.ne
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Networking & DNS.
33 articles on this topic
How to change a network interface name on CentOS/RHEL 7
Linux network interfaces are commonly named eth0, eth1, ... ethx. These names do not describe the interface hardware, so they do not tell us what kind of hardware eth0 or eth1 is…
How to fix bind hangs on generating rndc key
After setting up a DNS server, starting the named service may hang at Generating /etc/rndc.key:, as shown: [root@zm named]# /etc/init.d/named restart. Stopping named…
How to read pcap file in Linux CLI using tcpdump
pcap files from tcpdump or network devices are binary and cannot be read in ordinary text editors. tcpdump can read them directly from the Linux console.
List of default ports used by Zimbra Mail Server
The network ports used by Zimbra mail server fall into two groups. 1. External Access - Ports accessed by Clients or services outside the Zimbra system.
How to disable IPv6 on CentOS
There are several ways to disable IPv6. The recommended method is to edit /etc/sysctl.conf rather than disable the IPv6 module, which causes problems with SELinux and other components…
How to fix SMTP authen fail with error "curl_easy_perform: error(56)"
When SMTP authentication fails in Zimbra for every user and program, check the error log at /var/log/zimbra.log for an error like this: Jul 28 16:34:05 server saslauthd[33294]:
Enable SFTP logging transfer
SFTP, installed with OpenSSH, does not normally log activity. To log access and file changes, configure its Subsystem settings.
How to resolve yum error [Errno 14] PYCURL ERROR 6 - "Couldn't resolve host"
After installing CentOS, yum installs or updates may fail with "[Errno 14] PYCURL ERROR 6 - "Couldn't resolve host"", as in the example below: http://mirrors.psu.ac.th/pub
How to fix error: 97: Address family not supported by protocol on Zimbra
When starting the zimbra service, you may encounter the error message below: Starting nginx...nginx: [emerg] socket() [::]:7143 failed (97: Address family not supported by protocol) failed. Starting mta...Faile
How to fix "wget: unable to resolve host address" issue
If wget reports unable to resolve host address, first test network connectivity, then check whether wget is trying IPv6 on a machine without IPv6 access.
Definition of DNS status: NXDOMAIN, NOERROR and SERVFAIL
NXDOMAIN, NOERROR, and SERVFAIL are DNS query statuses. Understanding them helps interpret what happened when looking up domain records.
How to improve DNS lookups on Linux system
Listing multiple DNS servers in /etc/resolve.conf defines primary and secondary DNS servers. If the primary fails, the system switches to the secondary after a timeout.
How to fix high CPU usage problem on BIND (named)
BIND on CentOS 6 may use over 100% CPU when enabled with only zones and zone files configured. Check the logs, SELinux, and bind-chroot.
Displaying network traffic using tshark
TShark is a network protocol analyzer, the text-mode version of Wireshark, that captures live network packets and helps analyze traffic.
Guide for fix incoming mail from outside problems
When you have problems receiving email from outside, it can be difficult to determine where a message sent to your mail server has gone. First check the mail server logs, which can tell you…
How to limit SCP bandwidth
scp copies files between machines and can saturate links between sites. Use -l to limit bandwidth in Kbit/s.
How to install dig, host and nslookup commands on your system
If dig, host, or nslookup is missing on your Linux machine, you may have used a minimal installation on CentOS 6 or RHEL 6, or selected no packages during installation.
Setup a transparent proxy over ssl https with Squid
Most Squid transparent proxy tutorials cover only HTTP on port 80. Squid can also proxy HTTPS on port 443, but forwarding it directly to port 3128 does not work.
Squid fatal error: Could not determine fully qualified hostname
If a newly installed proxy server reports an error when starting Squid, check whether it can resolve its own hostname to an IP address.
How to integrate ClamAV into Pure-FTPd for virus scanning
One problem in website administration is a webmaster's computer becoming infected with a virus or Trojan without their knowledge. Uploaded scripts or HTML files may then contain malicious code.
Proxy Auto Configuration (PAC) - Proxy auto-config
This may be familiar to many readers, but it was new to me: using a proxy for selected websites while connecting directly to others with proxy auto-configuration.
Network Card Bonding On Red Hat Linux and CentOS
Channel bonding combines network interface cards to increase bandwidth, provide failover or load balancing, or use 802.3ad port trunking. It also supports VLANs, or 802.1q.
Get Squid Performance Statistic from command line
To inspect Squid's operation, use squidclient to request information from Squid. Squid is a proxy server program for Linux or Unix…
How to use wpa_cli command
wpa_cli is included in the wpa_supplicant package. It checks status and changes configuration, including trigger events and passphrases for wireless connections.
Set up your Linux for Wake On LAN (WOL)
Wake on LAN starts a server through a network command from another machine. Configure both the server receiving the wake command and the client sending it.
Configure VLAN devices over a bond interface
Linux supports VLAN networking through the 8021q driver. This example combines channel bonding and VLAN configuration.
Test the connectivity to server using netcat
Use netcat to test a connection by opening a socket on the server and connecting from a client on the network.
Other Virtual network interfaces go down when bring down virtual network interfaces
With multiple virtual network interfaces, bringing one interface down may also bring down others. This example uses eth0:0, eth0:1, eth0:2, and eth0:3.
Increase the maximum file descriptors for Squid
If Squid logs WARNING! Your cache is running out of filedescriptors in cache.log, it was compiled with a maximum of 1024 file descriptors.
Configure VSFTPD uses LDAP for authentication
vsftpd is a well-known FTP server included with many Linux distributions because it is stable, fast, and secure. It is widely used as an FTP server. Normally, vsftpd supports…
View extended information about network connections using netstat?
Use netstat to view network details with the command below. [root@example ~]# netstat -tuanpeeoT Active Internet connections (servers and established) Proto Recv-Q Send-Q Local…
Transparent proxy in squid 2.6
Transparent proxy configuration changed in Squid version 2.6 onward. It uses http_port 3128 transparent instead of the older configuration with many lines, as shown below…