Glossary
The jargon of operating-system isolation, in plain language. These definitions also pop up inline wherever the terms appear across the site.
- Egress
- Outbound network traffic. Egress control restricts where a sandbox may connect, so it cannot phone home or exfiltrate what it can read.
- Hypervisor
- The layer that gives a virtual machine its own kernel behind a hardware boundary, using the CPU's virtualization (Intel VT-x, AMD-V). KVM and Apple's Hypervisor.framework are hypervisors. Learn more →
- Inode
- The kernel's actual record for a file: a numbered structure holding its type, permissions, owner, size, and timestamps. A path is just a name that gets resolved to an inode; the inode is the real object the kernel then acts on. Learn more ↗
- Jailer
- A helper that wraps a VMM in namespaces, cgroups, a chroot, and a privilege drop, so a compromised VMM cannot reach the host. Firecracker ships one. Learn more →
- LSM
- Linux Security Module: a kernel hook (AppArmor, SELinux, Landlock) that decides whether an action on a specific object, a file or a socket, is allowed. Where seccomp filters the verb, an LSM filters the object. Learn more →
- Mandatory access control
- A model where the kernel, not the file's owner, enforces what a process may access. SELinux and AppArmor are mandatory access control systems.
- microVM
- A stripped-down virtual machine: its own guest kernel behind a hardware boundary, but with a minimal device model so it boots in about 100ms. Learn more →
- Prompt injection
- Getting an AI agent to follow instructions hidden in the content it reads (a malicious README, a web page, a dependency) instead of your intent. The realistic path to making an agent misbehave.
- SSRF
- Server-Side Request Forgery: tricking a program into making requests on your behalf, often to reach internal-only endpoints like a cloud metadata service.
- Syscall
- A request a running program makes to the OS kernel to do something it cannot do on its own: open a file, start a process, send a network packet. Syscalls are the verbs a program can ask the kernel for, and seccomp filters which ones it may call. Learn more ↗
- Virtio
- The standard paravirtualized device interface a VM uses to reach virtual disks, networks, and filesystems efficiently, instead of emulating real hardware.
- VMM
- Virtual Machine Monitor: the userspace program that drives the hypervisor and emulates the devices a guest sees. Firecracker and QEMU are VMMs.