docs(influxdb3 install): expand systemd runbook with day-2 commands (#7177)

* docs(influxdb3 install): expand systemd runbook with day-2 commands

Augment the existing systemd subsection in the Linux DEB/RPM install
guide with operationally-useful commands beyond start/status/logs:
stop, restart, is-enabled, is-active, follow-mode logs, packaged-unit
inspection (systemctl cat, systemctl show), and the edit-config-and-
restart workflow.

Verified service paths and behaviors against the v3.9.1 packaged
systemd unit (`influxdb3-enterprise.service`). Uses the existing
`influxdb3-{{< product-key >}}` convention so both Core and
Enterprise pages render with the correct unit name.

Closes influxdata/DAR#650

* docs(influxdb3 config-options): clarify how TOML interacts with env vars

Add a new "TOML configuration files (DEB/RPM installs)" subsection to
the config-options reference. The InfluxDB 3 systemd launcher reads
/etc/influxdb3/influxdb3-<product-key>.conf and converts each setting
to an INFLUXDB3_* environment variable before invoking
`influxdb3 serve` — the binary itself does not natively read TOML.
This means CLI flags still override TOML values, because they override
the env vars the file becomes.

Cross-reference the new section from the install page's
"Apply configuration changes" workflow.

Source: behavior described in influxdb3/src/commands/serve/cli_params/
tests.rs (test_config_file_cli_option_drift), confirming the
launcher-mediated TOML→env conversion at v3.9.1.

* docs(influxdb3 install): add sudo to systemctl status and journalctl

PR review feedback: `systemctl status` was inconsistently sudo'd
(missing in "Check status and logs", present in "Apply configuration
changes"). Adding `sudo` also guarantees full journal output for users
not in the systemd-journal group.

Apply the same fix to all three `journalctl` invocations for the same
journal-access reason. Leave `is-enabled`, `is-active`, `cat`, and
`show` as-is — these are pure metadata reads and don't touch journald.

* fix(install): repair four broken anchors/links flagged by link-checker

- TOML configuration files anchor: simplify heading to drop the
  "(DEB/RPM installs)" qualifier so the generated anchor matches the
  cross-reference link. Hugo strips the slash, so the qualifier
  produced "debrpm-installs" rather than "deb-rpm-installs".
- "Upgrade from Core" link path: drop the spurious /license/ segment;
  the actual page is at /admin/upgrade-from-core/. Note block is
  already gated to enterprise via show-in.
- "Download InfluxDB 3 binaries" link: was self-referential to the
  same section the reader is on. The actual download links are in
  the expand-wrapper directly below. Remove the redundant link, keep
  the prose.

* Update content/shared/influxdb3-cli/config-options.md

* Update content/shared/influxdb3/install.md

Author: jstirnaman

content/shared/influxdb3-cli/config-options.md

@@ -8,6 +8,25 @@
 Pass configuration options using either command options or environment variables.
 Command options take precedence over environment variables.
 
+### TOML configuration files
+
+DEB and RPM installs include a TOML configuration file at
+`/etc/influxdb3/influxdb3-{{< product-key >}}.conf`.
+The systemd launcher reads this file and converts each entry to an
+`INFLUXDB3_*` environment variable (the pattern is `INFLUXDB3_<KEY>`
+with hyphens replaced by underscores and uppercased) before invoking
+`influxdb3 serve`.
+
+`influxdb3 serve` does not yet natively read TOML; the file's effect is
+applied through the environment variables the launcher sets.
+CLI flags passed to `influxdb3 serve` still override values defined in
+the TOML file because they override the environment variables that
+file becomes.
+
+For day-to-day systemd operation — including the edit-and-restart
+workflow for applying changes — see
+[Run as a system service (Linux)](/influxdb3/version/install/#run-as-a-system-service-linux).
+
 ### Global vs serve-specific options
 
 Some options are **global** (specified before the command) while others are **serve-specific** (specified after `serve`):

content/shared/influxdb3/install.md

@@ -23,7 +23,7 @@
 > #### Upgrading from InfluxDB 3 Core?
 >
 > If you're currently running InfluxDB 3 Core and want to upgrade to {{% product-name %}},
-> see [Upgrade from Core](/influxdb3/version/admin/license/upgrade-from-core/)
+> see [Upgrade from Core](/influxdb3/version/admin/upgrade-from-core/)
 > for step-by-step instructions.
 
 > [!Note]
@@ -90,7 +90,7 @@ curl -O https://www.influxdata.com/d/install_influxdb3.sh \
 
 ### Download and install the latest build artifacts
 
-You can also download and install [{{% product-name %}} build artifacts](/influxdb3/version/install/#download-influxdb-3-{{< product-key >}}-binaries) directly:
+You can also download and install {{% product-name %}} build artifacts directly:
 
 {{< expand-wrapper >}}
 {{% expand "Linux binaries" %}}
@@ -240,19 +240,75 @@ On `systemd` systems, the `influxdb3-{{< product-key >}}` unit file is
 `enabled` on install, but the unit is not started in order to allow
 configuration.
 
-To start the database, enter the following commands:
+###### Start, stop, and restart
+
+> [!Note]
+> The following examples use `sudo` for systems that require elevated privileges.
+> On some systems (such as Amazon Linux or other RHEL-based distributions where you may already be running as root), you can omit `sudo` from the commands.
 
 ```bash
 # Start the service
-systemctl start influxdb3-{{< product-key >}}
+sudo systemctl start influxdb3-{{< product-key >}}
 
-# View status
-systemctl status influxdb3-{{< product-key >}}
+# Stop the service
+sudo systemctl stop influxdb3-{{< product-key >}}
 
-# View logs
-journalctl --unit influxdb3-{{< product-key >}}
+# Restart the service (use after configuration changes)
+sudo systemctl restart influxdb3-{{< product-key >}}
 ```
 
+###### Check status and logs
+
+```bash
+# Check status (sudo to ensure full journal output)
+sudo systemctl status influxdb3-{{< product-key >}}
+
+# Quick state checks (no sudo needed)
+systemctl is-enabled influxdb3-{{< product-key >}}
+systemctl is-active  influxdb3-{{< product-key >}}
+
+# Recent logs
+sudo journalctl --unit influxdb3-{{< product-key >}} -n 200 --no-pager
+
+# Follow logs
+sudo journalctl --unit influxdb3-{{< product-key >}} -f
+```
+
+###### Inspect the packaged unit
+
+The packaged unit configures security sandboxing for typical deployments
+(see [Manage security](/influxdb3/version/admin/security/)).
+To inspect the packaged unit and its resolved properties:
+
+```bash
+# Show the unit file
+systemctl cat influxdb3-{{< product-key >}}
+
+# Show all resolved properties (paths, environment, sandboxing options)
+systemctl show influxdb3-{{< product-key >}}
+```
+
+###### Apply configuration changes
+
+Edit the TOML configuration file and restart the service to apply
+changes:
+
+```bash
+sudoedit /etc/influxdb3/influxdb3-{{< product-key >}}.conf
+sudo systemctl restart influxdb3-{{< product-key >}}
+sudo systemctl status  influxdb3-{{< product-key >}}
+sudo journalctl --unit influxdb3-{{< product-key >}} -n 100 --no-pager
+```
+
+`influxdb3 serve` does not support configuration reload; a restart is
+required after editing the TOML file or changing environment variables.
+
+The TOML file is read by the systemd launcher and converted to
+`INFLUXDB3_*` environment variables before `influxdb3 serve` runs;
+CLI flags still override values from the TOML file.
+For details, see
+[TOML configuration files](/influxdb3/version/reference/config-options/#toml-configuration-files).
+
 ##### Run using SysV
 
 On SysV init systems, `influxdb3-{{< product-key >}}` is disabled on install