Processes

Processes have ids, PIDs. Processes can spawn other decendents, who inherit the environment variables of their parent process.

• sub processes can change variables, but do not effect their parent

source

• when program is executed, a special environment is created for it, containing everything it needs to run
• when a command is issued, a new process is started
• OS tracks rpocesses with five digit ID (pid)
• Foreground Processes take input from keyboard and output to screen (think commands)
• Background Processes run in background, you can run other commands while they're running
• each unix process has pid and parent process id (ppid), run ps -f for info
• when a child ps is killed, SIGCHLD is sent to the parent (for it to create a new ps or act)
• Daemon Processes are system-related background processes, have no controlling terminal

Anonymous Pipe

An anonymous pipe is a one-way FIFO channel for communication between processes.

• typically a parent program opens anonymous pipes, spawns child processes that inherit other ends of the pipes
  • or creates several processes and arranges them in a pipeline

File Descriptors

A handle is just an abstract reference to some resource outside the scope of your software (think like accessing memory in a database or from the OS). A File Descriptor is a type of handle

inode

Data structure that describes a filesystem object (file/directory), with metadata attributes, disk block location as well as the object's data

• must include size in bytes, device ID (containing inode), user ID of owner, group ID, file permissions mode, timestamp for last modified & accessed, link count for number of hard links