This comprehensive guide walks you through Linux user and group concepts, UID/GID identifiers, essential commands like useradd, groupadd, id, passwd, and su/sudo, plus configuration files and security practices for effective system administration.
This article explains how Linux processes inherit and manage user identities, detailing the roles of real, effective, and saved set user IDs, how they affect file access permissions, and demonstrates the execution flow of internal and external commands, including setuid examples.
This guide explains how to identify Linux accounts whose UID is 1000 or higher by parsing /etc/passwd with awk, then pipe the resulting usernames to xargs to invoke userdel ‑r for safe, automated removal of those users and their home directories.
This guide explains Linux's multi‑user architecture, the meaning of UID/GID, how to view and edit /etc/passwd and /etc/shadow, and provides step‑by‑step commands for creating, modifying, and deleting users and groups, including su and sudo usage.
This article explains how Linux processes inherit and use real, effective, and saved user IDs to enforce permission checks, covering the login sequence, UID inspection via /proc, set‑uid behavior, and the execution flow of external commands and shell scripts.
This article explains why Docker‑run creates directories owned by root, how missing user specifications cause permission denied errors for other applications, and provides step‑by‑step commands to identify the UID/GID and run containers with the correct non‑root user.
This article explains how Docker containers run processes as the host’s root user by default, how UID and GID are shared between host and container, demonstrates the security implications through demos with volume mounts, and shows how to change the container user via Dockerfile or the --user flag.
The article explains how to read an NFC card’s UID on Android, use it as a unique user identifier for login verification, and walks through required permissions, setting the activity launch mode to singleTop, designing the UI layout, handling NFC intents, converting the UID to a hex string, and debugging the implementation.
This article explains how to measure and analyze the power and network traffic consumption of a push SDK on Android devices, covering test preparation, the operations that generate power usage, methods to retrieve traffic data via ADB, script implementation, key testing points, encountered issues, and practical solutions.
This article explains how Android inherits Linux's UID/GID based permission model, details the sandbox isolation for apps, describes how system and app processes obtain their UID/GID, and shows how adb shell and framework permissions grant extensive access to the device.
This article explores Android’s sandbox mechanism, detailing how Linux‑based UID/GID permissions, file system rules, and permission groups control app isolation and access, with practical insights into adb shell behavior and permission granting.
This article explains how Linux server programs run as daemons, covering logging mechanisms, syslog usage, user and group IDs, process groups and sessions, resource limit management, and techniques for changing working directories and chrooting.
