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
The cgconfig Service
The cgconfig service installed with the libcgroup package provides a convenient way to create hierarchies, attach subsystems to hierarchies, and manage cgroups within those hierarchies. It is recommended that you use cgconfig to manage hierarchies and cgroups on your system.
The cgconfig service is not started by default on Red Hat Enterprise Linux 6. When you start the service with chkconfig, it reads the cgroup configuration file — /etc/cgconfig.conf. Cgroups are therefore recreated from session to session and become persistent. Depending on the contents of the configuration file, cgconfig can create hierarchies, mount necessary file systems, create cgroups, and set subsystem parameters for each group.
The default /etc/cgconfig.conf file installed with the libcgroup package creates and mounts an individual hierarchy for each subsystem, and attaches the subsystems to these hierarchies.
If you stop the cgconfig service (with the service cgconfig stop command), it unmounts all the hierarchies that it mounted.
Reference: http://redhat.com
D-Bus IPC Service (messagebus)
D-Bus is an IPC mechanism that provides a common channel for inter-process communication.
If no services which require D-Bus are in use, disable this service:
# chkconfig messagebus off
A number of default services make use of D-Bus, including X Windows, Bluetooth, and Avahi. For security its recommended that D-Bus and all its dependencies be disabled unless there is a mission-critical need for them.
Stricter configuration of D-Bus is possible and documented in the man page dbus-daemon(1). D-Bus maintains two separate configuration files, located in /etc/dbus-1/, one for system-specific configuration and the other for session-specific configuration.
Using pam deny.so to Quickly Deny Access to a Service
In order to deny access to a service SVCNAME via PAM, edit the file /etc/pam.d/SVCNAME . Prepend this line to the beginning of the file:
auth requisite pam_deny.so
Under most circumstances, there are better ways to disable a service than to deny access via PAM. However, this should suffice as a way to quickly make a service unavailable to future users (existing sessions which have already been authenticated, are not affected). The requisite tag tells PAM that, if the named module returns failure, authentication should fail, and PAM should immediately stop processing the configuration file. The pam deny.so module always returns failure regardless of its input.
HTTP Error 502 Bad Gateway, 503 Service Unavailable
This error is usually due to improperly configured proxy servers. However, the problem may also arise when there is poor IP communication amongst back-end computers, when the client’s ISP is overloaded, or when a firewall is functioning improperly.
The first step in resolving the issue is to clear the client’s cache. This action should result in the a different proxy being used to resolve the web server’s content.
503 Service Unavailable
This error occurs when the server is unable to handle requests due to a temporary overload or due to the server being temporarily closed for maintenance. The error signifies that the server will only temporarily be down. It is possible to receive other errors in place of 503.
