systemctl - Control the systemd system and service manager
systemctl may be used to introspect and control the state of the systemd(1) system and service manager.
systemd is a system and service manager for Linux operating systems. When run as first process on boot (as PID 1), it acts as init system that brings up and maintains userspace services.
Getting Help
systemctl -h
systemctl [OPTIONS...] {COMMAND} …
Query or send control commands to the systemd manager.
-h –help Show this help
–version Show package version
-t –type=TYPE List only units of a particular type
-p –property=NAME Show only properties by this name
-a –all Show all units/properties, including dead/empty ones
–failed Show only failed units
–full Don’t ellipsize unit names on output
–fail When queueing a new job, fail if conflicting jobs are
pendin
How to disable X Window System Listening
To prevent X.org from listening for remote connections, create the file /etc/X11/xinit/xserverrc and fill it with the following line:
exec X :0 -nolisten tcp $@
One of X.org’s features is the ability to provide remote graphical display. This feature should be disabled unless it is required. If the system uses runlevel 5, which is the default, the GDM display manager starts X safely, with remote listening disabled. However, if X is started from the command line with the startx command, then the server will listen for new connections on X’s default port, 6000.
How to confirm Existence and Permissions of System Log Files
For each log file LOGFILE referenced in /etc/syslog.conf or /etc/rsyslog.conf, run the commands:
# touch LOGFILE
# chown root:root LOGFILE
# chmod 0600 LOGFILE
Syslog will refuse to log to a file which does not exist. All messages intended for that file will be silently discarded, so it is important to verify that all log files exist. Some logs may contain sensitive information, so it is better to restrict permissions so that only administrative users can read or write logfiles.
Network Parameters for Hosts Only System
If the system is not going to be used as a firewall or gateway to pass IP traffic between different networks, then edit the file /etc/sysctl.conf and add or correct the following lines:
net.ipv4.ip forward = 0
net.ipv4.conf.all.send redirects = 0
net.ipv4.conf.default.send redirects = 0
These settings disable hosts from performing network functionality which is only appropriate for routers.
virtualization with Red Hat Enterprise Linux - System requirements.
This chapter lists system requirements for successfully running virtualization with Red Hat Enterprise Linux. Virtualization is available for Red Hat Enterprise Linux 5 Server.
The requirements for virtualization vary depending on the type of hypervisor. The Kernel-based Virtual Machine (KVM) and Xen hypervisors are provided with Red Hat Enterprise Linux 5. Both the KVM and Xen hypervisors support Full virtualization. The Xen hypervisor also supports Para-virtualization.
Minimum system requirements
6GB free disk space
2GB of RAM.
Recommended system requirements
6GB plus the required disk space recommended by the guest operating system per guest. For most operating systems more than 6GB of disk space is recommended.
One processor core or hyper-thread for each virtualized CPU and one for the hypervisor.
2GB of RAM plus additional RAM for virtualized guests.
