# Basics of Linux ### Process

# Process 
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- Running instance of a program in the computer's memory
                          - A non-running program is a file
                          - Isolated from other processes
                          - Has its own unique process identifier (PID)
                          - Has a parent process
                          - Can create child processes

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                        # Launching a process
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1. From the command-line
                        2. From another process

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                        # Launch a process: Command-line
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- The file must contain executable content, such as script or binary
                        - The file needs execute permission (`x`)
                        - The user must be part of the permitted group (`u`,`g` or `o`)
                        - By default processes launched from the command-line reserve the current session
                          - The process is launched in the background if the command ends in `&`
                        - The current session will be the parent process ID (PPID)

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                        # Launch a process: Another process
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- Scripts can call other commands or scripts
                        - The operating system may have processes running that can execute commands or scripts
                          - Init
                          - Cron
                        - Calling process will be the parent process ID (PPID)

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                        # Processes on a timeline
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                            <img src="/img/sld-linux-1-process-01.svg" alt="Processes on a timeline.">
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                        # Commands for running processes
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kill

pidof

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Report a snapshot of the current processes

Send a signal to a process

Find the process ID of a running program

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Thank you

Joona Tolonen

servicedesk@csc.fi