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/etc/hostname
/etc/timezone
/etc/fstab
/etc/resolv.conf
/etc/hosts
/etc/environment

Hostname

File(s)	Description
`/etc/hostname`	Contains the hostname of the system.

Timezone

File(s)	Description
`/etc/timezone` `/etc/adjtime` `/etc/localtime`	Contains the timezone of the system.

Mounted filesystems

File(s)	Description
Configuration: `/etc/fstab` Mount logs (such as `Mounting` operation / keyword): `/var/log/dmesg`	Contains information on the filesystems, their mountpoints, and mount options. Notably include the partition types (ext3 / ext4, etc.) of mounted filesystems.

DNS nameservers

File(s) Description

/etc/resolv.conf Contains the DNS nameservers and can be managed a number of ways:
- As a static file, with hardcoded DNS nameservers.
- By the DHCP daemon / client directly.
- By a middleman component between the network configuration services and the /etc/resolv file. They are several implementations of this intermediary: openresolv’s resolvconf package, Debian’s resolvconf package, systemd’s systemd-resolved service, etc.

The systemd-resolved daemon is configured through the /etc/systemd/resolved.conf file. This file contains the daemon parameters, DNS nameservers, fallback servers, and other DNS resolver configuration. The openresolv package stores the same information in the /etc/resolvconf.conf file.

The resolv.conf contain DNS nameserver entries, specified by the nameserver directive (such as nameserver 1.1.1.1), and can contain domain or search entries. A domain entry specifies which default domain name to append to names that do not end with a .. A search entry defines the list of domains to search when resolving a name.

File(s)	Description
`/etc/resolv.conf`	Contains the DNS nameservers and can be managed a number of ways: - As a static file, with hardcoded DNS nameservers. - By the `DHCP` daemon / client directly. - By a middleman component between the network configuration services and the `/etc/resolv` file. They are several implementations of this intermediary: `openresolv`’s `resolvconf` package, Debian’s `resolvconf` package, `systemd`’s `systemd-resolved` service, etc. The `systemd-resolved` daemon is configured through the `/etc/systemd/resolved.conf` file. This file contains the daemon parameters, DNS nameservers, fallback servers, and other DNS resolver configuration. The `openresolv` package stores the same information in the `/etc/resolvconf.conf` file. The `resolv.conf` contain DNS nameserver entries, specified by the `nameserver` directive (such as `nameserver 1.1.1.1`), and can contain `domain` or `search` entries. A `domain` entry specifies which default domain name to append to names that do not end with a `.`. A `search` entry defines the list of domains to search when resolving a name.

Static domain name resolutions (hosts)

File(s)	Description
`/etc/hosts`	Contains static domain name resolution(s) to map hostnames to IP addresses with out relying on `DNS` queries. Entries in the `/etc/hosts` take priority over `DNS` resolution.

System-wide environment variables

File(s) Description

/etc/environment
/etc/security/environ Contains, on some distributions, the system-wide environment variables, defined as key-value pairs.

The /etc/environment is notably linked to the Pluggable Authentication Modules (PAM) component. When a PAM-aware program (such as su or sudo) is executed, the program loads PAM, which in turn searches under /etc/pam.d for a configuration file with the same name as the launched program (such as /etc/pam.d/su). If the pam_env module is specified (i.e session required pam_env.so readenv=1), the environnement variables are loaded from the /etc/environment.

File(s)	Description
`/etc/environment` `/etc/security/environ`	Contains, on some distributions, the system-wide environment variables, defined as key-value pairs. The `/etc/environment` is notably linked to the `Pluggable Authentication Modules (PAM)` component. When a `PAM-aware` program (such as `su` or `sudo`) is executed, the program loads `PAM`, which in turn searches under `/etc/pam.d` for a configuration file with the same name as the launched program (such as `/etc/pam.d/su`). If the `pam_env` module is specified (i.e `session required pam_env.so readenv=1`), the environnement variables are loaded from the `/etc/environment`.

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