CentOS/RHEL 6

Question: How to create an lxc container using lxcbr0 and virbr0 network interfaces? LXC uses the virtualization management service to support network bridging for containers, libvirtd uses bridge network virbr0 and lxc-net.service uses bridge of lxcbr0. To start virbr0 bridge start libvirt service and create a container using network.link as virbr0: virbr0: flags=4163 mtu 1500 inet 192.168.122.x netmask 255.255.255.0 broadcast 192.168.1xx.2xx ether 52:54:00:be:71:21 txqueuelen 0 … [Read more...] about How to create LXC container using lxcbr0 and virbr0 in CentOS/RHEL

Question: How to Delete Duplicate Rules in Routing Policy Database? Use the IP Rule selector for deleting the specific IP Rule. The syntax for the command is as follows: # ip rule del pref [selector] 1. First, list the routing policy database: # ip rule list 0: from all lookup local 32760: from all to 10.0.0.10 lookup 220. 32761: from 10.0.0.10 lookup 220. 32762: from all to 172.16.0.0/23 lookup 210 32763: from 172.16.0.0/23 lookup 210 32764: from all to 10.0.0.10 … [Read more...] about How to Delete Duplicate Rules in Routing Policy Database in CentOS/RHEL

1. Password Expiration To set the default password expiration when creating new accounts on CentOS/RHEL, edit the /etc/login.defs file. PASS_MAX_DAYS 100 Which means the maximum number of days a password may be used. Please check man page of login.defs for more options that can be set in /etc/login.defs.: $ man login.defs 2. Password Complexity The PAM module pam_cracklib can be used to force password complexity requirements. The complexity can be specified with the following … [Read more...] about How to Customize Linux Password Expiration and Complexity Requirements

You would like to configure your sendmail server to masquerade the sender address to no-reply@target-domain.net when sending emails from it. The Solution Normally to masquerade a domain, the "MASQUERADE_AS" and "MASQUERADE_DOMAIN" is used in /etc/mail/sendmail.mc. But that will leave the user unchanged. With sendmail, you can change both the domain and username on a case-by-case basis using the genericstable feature. 1. make sure all the "MASQUERADE" items are commented out in … [Read more...] about How To Masquerade Sender Address In Sendmail in CentOS/RHEL

The Problem Assembling a BTRFS device during boot fails with error BTRFS: too many missing devices, writeable mount is not allowed The disks have been mistakenly deleted The Solution The missing disks in the raid array do not allow the filesystem to be mounted. Below are the logs from dmesg: [ 44.706956] btrfs: disk space caching is enabled [ 44.708006] btrfs: failed to read the system array on sdd1 [ 44.721272] btrfs: open_ctree failed [ 45.437152] nr_pdflush_threads exported in … [Read more...] about BTRFS: too many missing devices, writeable mount is not allowed

The Problem On a BTRFS file system, the df command shows that the total number of inodes is 0. The Used and Free numbers are 0. # df -i / Filesystem Inodes IUsed IFree IUse% Mounted on /dev/xvda2 0 0 0 - / Note: The above output is taken from a virtual machine. The Solution BTRFS does not use inodes in quite the same way as other filesystems, and it has no pre-determined limits, so it has nothing to count. The inode counts for BTRFS will always show … [Read more...] about Command ‘df -i’ Shows ‘Inode=0’ on BTRFS File System

In this example case /var/log/secure.log will be rotated daily and if the log file size exceeds 100mb rotate process will start. 1. By default system rotates all major OS logs by checking syslog file located in /etc/logrotate.d/ # cat /etc/logrotate.d/syslog /var/log/cron /var/log/maillog /var/log/messages /var/log/secure /var/log/spooler { sharedscripts postrotate /bin/kill -HUP 'cat /var/run/syslogd.pid 2> /dev/null' 2> /dev/null || true endscript } # 2. To add separate log … [Read more...] about How to Create a Custom Log File Rotation by logrotate in Linux

Question: How to use a FILE instead of directly providing the username/password while mounting CIFS share. Let us assume the below, The Windows Machine IP is "10.176.x.x" Windows Folder to be mounted is called 'data' Planning to Mount the Windows share to a Linux folder called '/mnt' The credential file created on Linux machine is called '/root/cifs_creds' Below are the entry inside the file: username=geek password=xxyyzz Now run the 'mount' command on Linux box as below: # … [Read more...] about How to Provide Credentials From a File While Mounting CIFS Share in Linux

The Problem Unable to start Nagios Network Monitoring service after reboot. -- var/log/messages ---- May 6 09:14:28 [hostname] nagios: Checking global event handlers... May 6 09:14:28 [hostname] nagios: Checking obsessive compulsive processor commands... May 6 09:14:28 [hostname] nagios: Checking misc settings... May 6 09:14:28 [hostname] nagios: Total Warnings: 0 May 6 09:14:28 [hostname] nagios: Total Errors: 0 May 6 09:14:28 [hostname] nagios: Things look okay - No serious problems … [Read more...] about Unable to start Nagios Service (CentOS/RHEL)