Device nodes on Unix-like systems do not necessarily have to correspond to physical devices. Nodes that lack this correspondence form the group of pseudo-devices.
They provide various functions handled by the operating system. Some of the most commonly-used (character-based) pseudo-devices include:
/dev/null
Accepts and discards all input; produces no output.（接受并丢弃所有输入；不产生输出）
/dev/zero
Produces a continuous stream of NUL (zero value) bytes.（产生持续的NUL字节流）
/dev/random
Produces a variable-length stream of pseudo-random or truly random numbers. (Blocking)（阻塞地生成变长伪随机或真随机数字流）(拓展阅读：/dev/random产生的随机数是否真随机？）
/dev/urandom
Produces a variable-length stream of pseudo-random numbers. (Non-Blocking)（非阻塞地生成变长伪随机数字流）
/dev/full
Produces a continuous stream of NUL (zero value) bytes when read, and returns a “disk full” message when written to.（被读取时，生成时序的NUL字节流；被写入时，返回“磁盘已满”信息）