1. The serial and parallel
Parallel interface: data you transmit simultaneously, which is characterized by fast transmission speed, but when the transmission distance, when the addition number of bits, resulting in a complicated and communication line cost.
Serial Communication: refers to a bit-sequence delivery of data, the communication line is characterized as simple as a pair of transmission lines can be two-way communication, and can use a telephone line, thereby greatly reducing the cost, especially for long-distance communications,
But the transmission rate is lower.
2. The process of state
R (running): process is running or waiting in the run queue.
S (Interrupt): the process is sleeping when the conditions for forming a signal is received or, if out of this state.
D (uninterruptible): Process system does not respond to asynchronous signals, even with the kill command nor can it be interrupted.
Z (zombie): the process has been terminated, but the process descriptor remain until the parent calls wait4 () function of the system
will process the release of
T (stop): the process after receiving a stop signal to stop running.
3. Service Management
systemctl start the service name to open service
systemctl stop service shut down the service name
systemctl restart the service name to restart the service
systemctl status Service Name Status
systemctl enable service name is added to the startup items
NOTE: systemd: (system daemon) is a software under linux init
systemctl: is the Configuration Tool
