CentOS/RHEL 5

A yum repository holds the rpms and metadata about the rpms. A yum repository must be configured in order to use yum on any yum based Linux system. This post provides steps to configure a yum repository for installing packages on CentOS/RHEL systems. Configuring yum repository server 1. Create a directory for you local repository, […]

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 […]

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 […]

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 […]

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> […]

The Problem While trying to create a logical volume, lvcreate fails with error “Volume “test_vg/lvol0″ Is Not Active Locally” even though the volume group is active, with an error output such as the following: # lvcreate -L 4G test_vg Volume “test_vg/lvol0” is not active locally. Aborting. Failed to wipe start of new LV. The Root […]

The ntpstat command output shows “unsynchronised”: # ntpstat unsynchronised time server re-starting The “ntpq -p ” command output shows none of ntp servers is chosen: # ntpq -p ========================================== remote refid st t when poll reach delay offset jitter =============================================== ntp-server .INIT. 16 u – 16 0 0.000 0.000 0.000 ntp-server .INIT. 16 u – […]

Question: How to view the system-wide swap usage on a CentOS/RHEL server via the top command to identify the highest consumers. Below are the steps for CentOS/RHEL 5 and 6 which are the same, followed by CentOS/RHEL 7 as they differ on this release: NOTE: Performing this task will not cause any changes to top […]

The Problem A Linux OS failed bootup, from console log we can see all goes well in the very beginning, kernel loaded and init scripts were running OK. But suddenly the Linux OS was shutting down (received TERM signal) after auditd daemon started. … dracut: Switching root mount: mount point /proc/bus/usb does not exist Welcome […]