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# /etc
**/etc** holds system-wide configuration files. Every file in `/etc` is a plain text file or a directory of text files; no binaries live here. Editing a file in `/etc` changes the behaviour of the corresponding service or subsystem for all users on the machine. User-level configuration lives in dotfiles under `$HOME`, not in `/etc`.

```
/etc/fstab          filesystem mount table; read at boot
/etc/passwd         user account database (no passwords; those are in /etc/shadow)
/etc/shadow         hashed passwords; readable only by root
/etc/group          group database
/etc/hostname       the machine's hostname
/etc/hosts          static hostname-to-IP mappings; consulted before DNS
/etc/resolv.conf    DNS resolver configuration: nameserver addresses, search domains
/etc/os-release     distribution identity: NAME, VERSION_ID, etc.
/etc/fstab          filesystem table: what to mount, where, and with what options
/etc/ssh/           SSH daemon and client configuration
/etc/sudoers        rules for which users may run commands as root via sudo
/etc/crontab        system-wide cron jobs
/etc/apt/           APT package manager configuration and source lists (Debian/Ubuntu)
/etc/systemd/       systemd unit overrides and system configuration
```

Most services follow the convention of placing their configuration in `/etc/<service>/` or `/etc/<service>.conf`. A file dropped into `/etc/<service>.d/` typically overrides the main config without editing it directly, which makes package manager upgrades cleaner — the package can update the main file while the local override remains untouched.