add

technology/applications/media/yt-dlp.md

@@ -132,11 +132,11 @@ The available fields are:
 -   `uploader` (string): Full name of the video uploader
 -   `license` (string): License name the video is licensed under
 -   `creator` (string): The creator of the video
--   `timestamp` (numeric): UNIX timestamp of the moment the video became available
+-   `timestamp` (numeric): [UNIX timestamp](../../linux/UNIX%20Timestamp.md) of the moment the video became available
 -   `upload_date` (string): Video upload date in UTC (YYYYMMDD)
--   `release_timestamp` (numeric): UNIX timestamp of the moment the video was released
+-   `release_timestamp` (numeric): [UNIX timestamp](../../linux/UNIX%20Timestamp.md) of the moment the video was released
 -   `release_date` (string): The date (YYYYMMDD) when the video was released in UTC
--   `modified_timestamp` (numeric): UNIX timestamp of the moment the video was last modified
+-   `modified_timestamp` (numeric): [UNIX timestamp](../../linux/UNIX%20Timestamp.md) of the moment the video was last modified
 -   `modified_date` (string): The date (YYYYMMDD) when the video was last modified in UTC
 -   `uploader_id` (string): Nickname or id of the video uploader
 -   `channel` (string): Full name of the channel the video is uploaded on

technology/bsd/gunion.md

@@ -0,0 +1,33 @@
+---
+obj: filesystem
+---
+
+# gunion
+The `gunion` utility is used to track changes to a read-only disk on a writable disk on [FreeBSD](FreeBSD.md). Logically, a writable disk is placed over a read-only disk. Write requests are intercepted and stored	on the writable disk. Read requests are first checked to see if they have been written on the top (writable disk) and if found are returned. If they have not been written on the top disk, then they are read from the lower disk.
+
+## Usage
+**Create a union disk:**
+```shell
+gunion create [-v] [-o offset] [-s size] [-S secsize] [-Z gunionname] upperdev lowerdev
+```
+
+**Destroy union disk:**
+```shell
+gunion destroy [-fv] prov ...
+```
+
+**Revert changes made:**
+```shell
+gunion revert [-v] prov ...
+```
+
+**Commit changes made to lower disk:**
+```shell
+gunion commit [-frv] prov ...
+```
+
+**See status:**
+```shell
+gunion list
+gunion status
+```

technology/linux/UNIX Timestamp.md

@@ -0,0 +1,33 @@
+---
+obj: concept
+---
+
+# UNIX Timestamp
+A Unix timestamp is a way to represent a point in time, defined as the number of seconds that have elapsed since the Unix epoch. The Unix epoch is defined as 00:00:00 UTC on January 1, 1970.
+
+## Usage
+Unix timestamps are commonly used in computing systems to record and calculate time-based events. They are particularly useful for tasks such as:
+- Logging events: Recording the time when an event occurs.
+- Date arithmetic: Calculating time differences between two Unix timestamps.
+- Scheduling tasks: Determining when a task should be executed based on a Unix timestamp.
+
+## Conversion
+Unix timestamps can be converted to human-readable date and time formats using various programming languages and tools. For example, in Unix-based systems, the `date` command can be used to convert a Unix timestamp to a formatted date:
+```shell
+date -d @<timestamp>
+```
+
+Replace `<timestamp>` with the Unix timestamp you want to convert.
+
+## Examples
+- The Unix timestamp `0` represents the Unix epoch, which is January 1, 1970, at 00:00:00 UTC.
+- The current Unix timestamp can be obtained using various programming languages and tools. For example, in [Python](../dev/programming/languages/Python.md):
+
+```python
+import time
+current_timestamp = int(time.time()) print(current_timestamp)
+```
+
+## Considerations
+- **Leap seconds**: Unix timestamps do not account for leap seconds, which are occasionally added to Coordinated Universal Time (UTC) to keep it in sync with the Earth's rotation. As a result, there may be slight discrepancies between Unix timestamps and true time.
+- **Range limitations**: The range of Unix timestamps is limited by the number of bits used to represent them. For a 32-bit signed integer, the range is approximately from 1901-12-13T20:45:52 UTC to 2038-01-19T03:14:07 UTC. However, many systems now use 64-bit integers, which extend the range significantly.