Process
A process in UNIX/Linux is a running instance of a program.
Identifiers
Here are the different identifiers for a given process:
| Identifier | Full Name | Scope | Purpose | Example |
|---|---|---|---|---|
| PID | Process ID | Per process | Unique identifier of a process | 4123 |
| PPID | Parent Process ID | Per process | PID of the process’s parent | 4120 |
| UID | User ID | Per process | User owner identity | 1000, 0 (root) |
| GID | Group ID | Per process | Primary group identity | 1000 |
| PGID | Process Group ID | Per process group | Groups related processes together | Shell pipelines |
| SID | Session ID | Per session | Identifies a login/session leader | Terminal session |
| TID | Thread ID | Per thread | Identifies a specific thread | Linux thread identifier |
| TTY | Terminal ID | Per process | Controlling terminal | /dev/pts/0 |