Moving a datafile from the file system can be achieved in two ways. 1. While the database is shutdown (in mount stage). 2. While the database is running (with the selected tablespace offline). While the database is shutdown (in mount stage) Moving oracle datafile while the database is in mount stage is performed in the […]
Archives for August 2016
RHEL 7 – RHCSA Notes : Create hard and soft links.
RHEL 7 – RHCSA Notes (Cheat Sheets) Soft links As shown in the diagram soft links or symbolic links simply points to another file. It only contains the pathname of the file to which it is pointing 1. Creation method # touch file # ln -s file link # ls -l -rw-r–r– 1 root root […]
CentOS / RHEL 7 : How to boot into Rescue Mode or Emergency Mode
The post explains how to bootup RHEL 7 system into rescue mode or emergency mode. In RHEL7, both rescue mode and emergency mode are systemd targets which replaced the concept of runlevels in previous linux versions. Rescue mode Rescue mode is equivalent to single user mode and requires the root password. Rescue mode allows you […]
How To Check World Wide Port Names (WWPN) of Tape Drives Attached to Linux host
Use the command ‘cat /proc/scsi/scsi‘ to check attached scsi devices. Below example shows IBM Ultrium generation 6 (LTO-6) Tape Drives attached to this Linux system. # cat /proc/scsi/scsi Attached devices: Host: scsi10 Channel: 00 Id: 00 Lun: 00 Vendor: IBM Model: ULT3580-TD6 Rev: F9A0 Type: Sequential-Access ANSI SCSI revision: 06 Host: scsi3 Channel: 00 Id: […]
Determining which network interface will be used for jumpstart installation / network boot
When network booting, the first part of the process is for the Client system to send out an Reverse Address Resolution Protocol request (RARP request) to request the corresponding IP address from the boot server. It’s important to know which interface will be used, as this can influence which ethernet address is sent onto the […]
How to allow only specific non-root user(s) to use crontab
From the manpage of crontab command: If the cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the cron.allow file does not exist but the cron.deny file does exist, then you must not be listed in the cron.deny file in order to use this command. […]
How to prevent non-root user from creating crontab entry
Often this is a requirement in production environments to disable the non-root users to create any crontab entry. There are three ways to achieve this : 1. Disable non-root user ssh to system, then non-root user is not able to use shell at all. Refer to this post for procedure. 2. Add user into file […]
RHEL 7 – RHCSA Notes – input / output redirection
RHEL 7 – RHCSA Notes (Cheat Sheets) Three standard file descriptors : 1. stdin 0 – Standard input to the program. 2. stdout 1 – Standard output from the program. 3. stderr 2 – Standard error output from the program. Purpose Command redirect std output to filename > filename or 1> filename append std out to filename […]
M-Series Servers : How to reset XSCF password
Follow the procedure below in case you have forgotten or want to reset the existing XSCF user password. (This procedure needs the user to be physically present at the server) 1. Connect directly to the serial port using the serial cable and a laptop. 2. Configure the settings on the terminal program you are using […]
CentOS / RHEL 7 : Tips on Troubleshooting NTP / chrony Issues
The chrony service does not change the time The often misconception is that the chrony service is setting the time to the one given by the NTP server. This is incorrect – what actually happens is that based on the answer from the NTP server, chrony just tells the system clock to go faster or […]