Introduction - A packet filtering firewall reads incoming network packets and filters (allows or denies) each data packet based on the header information in the packet. The Linux kernel has built-in packet filtering functionality called Netfilter. - Two services are available in RHEL 7 to create, maintain, and display the rules stored by Netfilter: 1. firewalld 2. iptables - In RHEL 7, the default firewall service is firewalld. - firewalld is a dynamic firewall manager which supports … [Read more...] about CentOS / RHEL 7 : Beginners guide to firewalld
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CentOS / RHEL : Converting an Existing Root Filesystem to LVM Partition
Question: Root Filesystem is full and it is not LVM. We need to move this to new partition which is LVM. How this can be achieved? Answer : Procedure to convert an existing root file system on a normal disk partition to LVM volume is as follows : 1. First Create an LVM partition: Select a free disks and create an LVM partition on it. # pvcreate /dev/sdb1 # vgcreate vg_new_root /dev/sdb1 # lvcreate -L 4G -n lv0 vg_new_root 2. Format this new LVM partition with ext3 or ext4 (or as … [Read more...] about CentOS / RHEL : Converting an Existing Root Filesystem to LVM Partition
Linux / UNIX : How to send mails with attachments using mailx command
Question : How to send email with attachments from Linux machine using mailx command ? Answer : Basic syntax to send emails from linux machine using mailx command is show below : # echo "this is the body of the email" | mailx -vvv -s "test mail" -r "From" -S smtp="your-smtp" someone@address here, -vvv = Verbosity. -s = Specifies the subject. -r = Email sent from. -S = Specifies the smtp server. Method 1 : using uuencode (old method) If the mailx … [Read more...] about Linux / UNIX : How to send mails with attachments using mailx command
UNIX / Linux : Send mail with attachment using mutt
What is mutt Mutt is a text-based mail client. Mutt is known for being a fast and highly configurable mail client, and since it is text-based, it’s ideal for checking email quickly over SSH. Installing mutt To install mutt using yum : # yum install mutt ... ======================================================================================== Package Arch Version Repository … [Read more...] about UNIX / Linux : Send mail with attachment using mutt
CentOS / RHEL : How to add, delete and display LVM tags
What is LVM tag In a case where you want that only a particular set of logical volumes to be activated and available during boot, lvm tags can come in handy. Lvm tags can allow these tags to be marked beforehand and the effect achieved. Configuration file Navigate to the section show below in the configuration file /etc/lvm/lvm.comf : # vi /etc/lvm/lvm.conf # If volume_list is defined, each LV is only activated if there is a # match against the list. # # "vgname" and … [Read more...] about CentOS / RHEL : How to add, delete and display LVM tags
CentOS / RHEL 7 : How to Create and Remove the LVM Mirrors Using lvconvert
When you convert a linear volume to a mirrored volume, you are basically creating an extra mirror copy for an existing volume. This means that your volume group must contain the devices and space for the mirrors and for the mirror log. If losing a copy of a mirror, LVM converts the volume to a linear volume so that you still have access to the volume. And Option '[ -m | --mirrors ]' specifies the degree of the mirror you wish to create. For example: "-m 1" would convert the original … [Read more...] about CentOS / RHEL 7 : How to Create and Remove the LVM Mirrors Using lvconvert
RHEL 7 – RHCSA Notes – Set enforcing and permissive modes for SELinux
RHEL 7 – RHCSA Notes (Cheat Sheets) SELinux modes SELinux gives that extra layer of security to the resources in the system. It provides the MAC (mandatory access control) as contrary to the DAC (Discretionary access control). Before we dive into setting the SELinux modes, let us see what are the different SELinux modes of operation and how do they work. SELinux can operate in any of the 3 modes : 1. Enforced : Actions contrary to the policy are blocked and a corresponding event is logged … [Read more...] about RHEL 7 – RHCSA Notes – Set enforcing and permissive modes for SELinux
RHEL 7 – RHCSA Notes – Create and manage Access Control Lists (ACLs)
RHEL 7 – RHCSA Notes (Cheat Sheets) The file access control lists (FACLs) or simply ACLs are the list of additional user/groups and their permission to the file. Although the default file permissions does their jobs perfectly, it does not allow you to give permissions to more than one user or one group on the same file. How to know when a file has ACL attached to it ls -l command would produce a output as show below. Note the + sign at the end of the permissions. This confirms that the … [Read more...] about RHEL 7 – RHCSA Notes – Create and manage Access Control Lists (ACLs)
CentOS / RHEL : How to change password hashing algorithm
authconfig The Linux user password hashing algorithm is also configurable. Use the authconfig command to determine the current algorithm being used, or to set it to something different. To determine the current algorithm: # authconfig --test | grep hashing password hashing algorithm is sha512 Change the hashing algorithm To change the algorithm, use the --passalgo option with one of the following as a parameter: descrypt, bigcrypt, md5, sha256, or sha512, followed by the --update … [Read more...] about CentOS / RHEL : How to change password hashing algorithm
RHEL 7 – RHCSA Notes : Change passwords and adjust password aging for local user accounts
RHEL 7 – RHCSA Notes (Cheat Sheets) Password configuration password aging requires users to change their password periodically. Use the chage to configure password expiration. The syntax is : # chage [options] user_name - When you fire the command chage, the currently set options are displayed as well. # chage oracle Changing the aging information for oracle Enter the new value, or press ENTER for the default Minimum Password Age [14]: Maximum Password Age [30]: Last Password … [Read more...] about RHEL 7 – RHCSA Notes : Change passwords and adjust password aging for local user accounts