The ask is to remove the default rescue image that gets installed when you install a CentOS/RHEL 7 system. To list out the rescue image under /boot directory : [root@geeklab ~]# ls -lrt /boot total 135164 -rw-------. 1 root root 3113253 Nov 22 2016 System.map-3.10.0-514.el7.x86_64 -rw-r--r--. 1 root root 137696 Nov 22 2016 config-3.10.0-514.el7.x86_64 -rwxr-xr-x. 1 root root 5392080 Nov 22 2016 vmlinuz-3.10.0-514.el7.x86_64 -rw-r--r--. 1 root root 277953 Nov 22 2016 … [Read more...] about CentOS / RHEL 7 : How to remove rescue image using grubby
Linux interview questions – Special permissions (SUID, SGID and sticky bit)
There are two special permissions that can be set on executable files: Set User ID (setuid) and Set Group ID (sgid). These permissions allow the file being executed to be executed with the privileges of the owner or the group. Similarly, there are two special permissions for directories: the sticky bit and the setgid bit. Below are few of the most commonly asked Linux interview questions on the special permissions like SUID, SGID and sticky bit. What is Set User ID (setuid)? SUID is a … [Read more...] about Linux interview questions – Special permissions (SUID, SGID and sticky bit)
lvremove Command Fails With Error “LVM – Can’t remove open logical volume”
You want to delete a logical volume but, when running the command "lvremove", you get the following output: # umount /data # lvremove /dev/vg1/lv1 Can't remove open logical volume "lv1" Solution The above error usually means that the volume is still in use by some process. To find the process that is keeping the logical volume open, follow the steps below. 1. Find the major,minor number corresponding to the Logical Volume: # dmsetup info -c | grep [lvname] For Example: # dmsetup … [Read more...] about lvremove Command Fails With Error “LVM – Can’t remove open logical volume”
Yum Command Fails with “Another app is currently holding the yum lock” in CentOS/ RHEL 7
While issuing any yum command, you would get an error shown below: # yum list Loaded plugins: fastestmirror, langpacks Existing lock /var/run/yum.pid: another copy is running as pid 13023. Another app is currently holding the yum lock; waiting for it to exit... The other application is: PackageKit Memory : 26 M RSS (430 MB VSZ) Started: Sat Sep 30 18:31:21 2017 - 00:33 ago State : Sleeping, pid: 13023 The error indicates that another instance is running for the yum … [Read more...] about Yum Command Fails with “Another app is currently holding the yum lock” in CentOS/ RHEL 7
What causes iptables to load every time after a reboot even when it’s completely turned off
Question : Even though iptables is turned OFF using 'chkconfig --level 345 iptables off', 'service iptables status' still displays some iptables rules after every reboot. Answer The Libvirtd process will add iptables rules into iptables when starting libvirtd. iptables will run when starting libvirtd, even if iptables was disabled before. These rules will not impact firewall configuration for the physical network. If xen environment is not used, these rules are not needed at all. In a … [Read more...] about What causes iptables to load every time after a reboot even when it’s completely turned off
CentOS / RHEL : iptables troubleshooting guide
The iptables utility controls the network packet filtering code in the Linux kernel. The iptables feature is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel. The post discusses the most commonly encountered issues with iptables and how to resolve them. iptables rules do not load after a reboot you have set and saved iptables firewall rules and they are still not loaded after a reboot. After a reboot, the iptables rules are not loaded, and … [Read more...] about CentOS / RHEL : iptables troubleshooting guide
CentOS / RHEL 6 : How to change the verbosity of debug logs during booting
Removing the rhgb and the quiet kernel command-line parameters, either by editing the /boot/grub/grub.conf file or by using the grub editing mode during boot. Replace these parameters with loglevel parameter. This change is generally sufficient to provide as much data as is needed to debug a boot failure. The option rhgb is used for graphical boot-up and the quiet option eliminates most of the boot messages. what loglevels are available Removing rhgb quiet attributes, increases the … [Read more...] about CentOS / RHEL 6 : How to change the verbosity of debug logs during booting
Oracle Database interview questions – Privileges And Roles
What is a privieldge? A privilege is the right to execute a particular type of SQL statement. It can allow a user to access database objects or execute stored programs that are owned by another user or to perform system level actions. There are two types of privileges: system privileges schema object privileges What are system privileges? The system privileges are not related to a certain object. They control the ability of a user to perform system level actions such as connecting to … [Read more...] about Oracle Database interview questions – Privileges And Roles
CentOS / RHEL 5, 6 : how to disable NetworkManager
What is NetworkManager? - NetworkManager is a dynamic network control and configuration system that attempts to keep network devices and connections up and active when they are available. - NetworkManager consists of a core daemon, a GNOME Notification Area applet that provides network status information, and graphical configuration tools that can create, edit and remove connections and interfaces. - NetworkManager can be used to configure the following types of connections: Ethernet, … [Read more...] about CentOS / RHEL 5, 6 : how to disable NetworkManager
Solaris : How to include date and timestamp in bash shell command history
Here is a small note on how to enable date and timestamp in shell command history on a Solaris system. In some vendor implementations of ksh, the EXTENDED_HISTORY variable can be set. However, the Solaris ksh does not implement EXTENDED_HISTORY. There are no provisions for providing date or timestamps in the ksh history. Setting date and timestamp in bash shell command history If date and time are required, use bash and set the HISTTIMEFORMAT variable. For example: # export … [Read more...] about Solaris : How to include date and timestamp in bash shell command history