By default, RHEL 7 uses the FirewallD service to provide network security. Firewalld may not be to everyone’s liking and you may prefer iptables. FirewallD must be stopped and disabled when using the iptables service. The posts outlines the steps to disable firewalld and enable iptables in CentOS/RHEL 7. Stop and disable firewalld 1. To […]
Archives for March 2018
Linux OS Service ‘yppasswdd’
The yppasswdd service executes the yppasswdd daemon. The yppasswdd is a part of NIS (Network Information Service formerly Yellow Pages) server. This server allows users to change their password on a NIS server from a NIS client. The service must be run on the NIS master server for that NIS domain in conjunction with ypserv, […]
LVM ISCSI Physical Volume Not Available After Server Reboot
Problem 1 After a reboot the LVM volumes located on iscsi disks are not activated. Manually activating with “lvchange -ay” works fine. Using the _netdev option in /etc/fstab LVM is started before network initialisation is complete, thus the iscsi disks are not detected by the OS. Use the “_netdev” mount option to instruct the system […]
ZFS destroy error “cannot determine dependent datasets: recursive dependency”
Problem In the following case, the origin of clone (datapool/ds1) is a snapshot of its descendant (datapool/ds1/ds2). # zfs get -r origin datapool NAME PROPERTY VALUE SOURCE datapool/ds1 origin datapool/ds1/ds2@snap – datapool/ds1/ds2 origin – – datapool/ds1/ds2@snap origin – – To destroy datapool/ds1/ds2, its snapshot datapool/ds1/ds2@snap needs to be destroyed. To destroy datapool/ds1/ds2@snap, its dependent clone […]
How to enable XDMCP in GNOME Display Manager (gdm) for Solaris 10,11
This post describes how to enable XDMCP, which is disabled by default, in the GNOME Display Manager (gdm). XDMCP, or X Display Manager Control Protocol, allows login to gdm from remote X servers. For Solaris 10 1. Change the default “Enable=false” to “Enable=true” in the [xdmcp] section of /etc/X11/gdm/gdm.conf: # vi /etc/X11/gdm/gdm.conf [xdmcp] Enable=true 2. […]
How to create and mount filesystems in Linux
File System Types Creating a file system writes information to the device and creates order of the empty space. This file system–related data consumes a small percentage of the space. The remaining space on the disk drive is split into small, consistently sized segments called blocks. Linux supports a number of file system types, some […]
Sample /etc/mke2fs.conf file
Below is a sample /etc/mke2fs.conf file from an CentOS 7 system. # cat /etc/mke2fs.conf [defaults] base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr default_mntopts = acl,user_xattr enable_periodic_fsck = 0 blocksize = 4096 inode_size = 256 inode_ratio = 16384 [fs_types] ext3 = { features = has_journal } ext4 = { features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize,64bit inode_size = 256 } ext4dev = { features […]
Beginners Guide to User and Group Administration in Linux
Each user in Linux has a unique user ID (UID), which is an ordinary integer number, and an associated username. Users log in by using their usernames, but the system uses the associated UIDs. Each user account also has a home directory and a login shell. When users log in, they are placed in their […]
Understanding The sysfs File System (/sys) in Linux
In addition to /proc, the kernel also exports information to another virtual file system called sysfs. sysfs is used by programs such as udev to access device and device driver information. The creation of sysfs helped clean up the proc file system because much of the hardware information has been moved from proc to sysfs. […]
Understanding The /proc File System
The proc file system contains a hierarchy of special files that represent the current state of the kernel. It is named after its original purpose, which is an interface to the structures within running processes to support debugging tools. Linux adopted this from Solaris but also added the interface to the kernel. The proc file […]