User Space

Core Idea

User space is where normal programs run: shells, editors, git, curl, Python, Caddy, and your own scripts.

Why It Exists

User-space programs have less privilege than the kernel. They ask the kernel to open files, create processes, allocate memory, and use the network. The kernel enforces permissions and isolation.

Course Examples

ps -u "$USER" -o pid,comm,args | head
which bash
which curl
systemctl --user status site.service

Your systemd user service is a user-space process managed by your user account. It is not a root-managed system service.

User Space Boundaries

• Your files live under your home directory unless explicitly shared.
• Your processes run as your user unless started by another account.
• Your services use systemctl --user when managed by your user account.
• You do not install system packages or edit system service units without admin involvement.

Common Confusions

• User space does not mean graphical desktop. Server commands are user-space programs too.
• A user-space program can still be a server process.
• A process can fail because user-space configuration is wrong even when the kernel is fine.
• sudo changes privilege. It is not the normal path for this course.

Proof Check

Run ps -u "$USER" -o pid,comm,args | head. Name three user-space processes owned by you.

Docs Pointers

• Run man ps.
• Read Kernel, Syscall, and Server.
• Read Arch Wiki: systemd/User as reference, not as an instruction to change system policy.