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The major changes released with Red Hat Enterprise Linux 7 (beta) and Fedora 19 Linux server distributions are chronicled in the seventh edition of A Practical Guide to Fedora and Red Hat Enterprise Linux.
We spoke with the book's author, Mark Sobell, about some of the major changes in RHEL 7 and Fedora 19 Linux distributions. Sobell, president of the Linux/Unix consulting firm Sobell Associates Inc., updated the practical guide after two years to include these new details.
How does firewalld differ from its predecessor iptables service for firewall configuration?
Mark Sobell: Reloading the iptables service frequently broke established connections. The firewalld service does not need to be reloaded with every change; it accepts changes to the firewall while it is running.
The firewalld daemon introduces a level of abstraction that makes setting up a Linux firewall simpler and more intuitive. Instead of writing firewall rules as iptables, firewalld uses firewall-config [graphical user interface] or firewall-cmd [command-line interface] to set up a firewall.
D-bus is an interprocess communication system -- also called a message bus system -- that allows applications and processes to communicate and request services over a bus. The d-bus service, which runs dbus-daemon, notifies processes of events, [such as] when a new device is added or when a user logs in. The firewalld daemon's d-bus interface allows it to communicate with processes and also allows applications, daemons and administrators to enable or disable a firewalld feature. These features include opening ports, forwarding ports or packets and performing more advanced tasks.
As the default file system, what does XFS bring to the party in RHEL 7?
Sobell: XFS is a high-performance, journaling, 64-bit file system created by Silicon Graphics Inc. It supports file systems as large as 64 exabytes, containing files up to 8 exabytes in size and directory structures with tens of millions of entries. XFS allows you to defragment and expand a mounted, active file system and provide backup and restore facilities specific to XFS.
Compared to other Linux file systems, XFS improves performance -- especially for large files -- by using B+ trees that contain metadata that describe extents. It also supports parallel (simultaneous) I/O on multiple application threads, enhancing file system throughput on multiprocessor systems, with better throughput on multi-device files than previous generations of RHEL and Fedora.
What are the differences between system init daemon and SysVinit daemon?
Sobell: The RHEL 6 Upstart init daemon is gone. RHEL 7, Debian and Ubuntu have moved to systemd, so life will be much easier for Linux administrators who go between systems.
In Fedora, the systemd init daemon has matured quite nicely over the past couple of years. For a typical system administrator, the changes are mostly about how to control the daemons. A new systemctl command replaces chkconfig and service, although scripts allow you to still use the legacy commands.
Fedora has a nice cheat sheet: http://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet.
Editor's note: This interview is in relation to A Practical Guide to Fedora and Red Hat Enterprise Linux, Seventh Edition, authored by Mark Sobell, published by Pearson/Prentice Hall Professional, January 2014, ISBN 978-0-13-347743-6, Copyright 2014 Mark G. Sobell.