In computer programming, a sentinel node is a specifically designated node used with linked lists and trees as a traversal path terminator. This type of node does not hold or reference any data managed by the data structure. Benefits
Sentinels are used as an alternative over using NULL as the path terminator in order to get one or more of the following benefits:

Marginally increased speed of operations
Increased data structure robustness (arguably)

Drawbacks
Marginally increased algorithmic complexity and code size. If the data structure is accessed concurrently (which means that all nodes being accessed have to be protected at least for “read-only”), for a sentinel-based implementation the sentinel node has to be protected for “read-write” by a mutex. This extra mutex in quite a few use scenarios can cause severe performance degradation. One way to avoid it is to protect the list structure as a whole for “read-write”, whereas in the version with NULL it suffices to protect the data structure as a whole for “read-only” (if an update operation will not follow). The sentinel concept is not useful for the recording of the data structure on disk. Examples
Search in a linked list
Below are two versions of a subroutine (implemented in the C programming language) for looking up a given search key in a singly linked list. The first one uses the sentinel value NULL, and the second one a (pointer to the) sentinel node Sentinel, as the end-of-list indicator. The declarations of the singly linked list data structure and the outcomes of both subroutines are the same.
Nix or NIX may refer to:

Places
Nix, Alabama, an unincorporated community, United States
Nix, Texas, a ghost town in southwestern Lampasas County, Texas, United States
Nix (moon), a moon of Pluto

People
Nix (surname), listing people with the surname

In science and technology
Nix (gene), a pro-apoptotic gene
Norwegian Internet Exchange (NIX), an Internet exchange point in Oslo
Neutral Internet Exchange of the Czech Republic, the Internet exchange point in Prague
Nix package manager, a "purely functional" package and configuration manager for computer systems
Unix-like, abbreviated *nix or nix

Codes
Nioro Airport, Mali (IATA airport code: NIX)
Hema language, (ISO 639-3 code: nix)

Other uses
Nix Federal Building, a historic building in Philadelphia, Pennsylvania
Nix Professional Building, a hospital in San Antonio, Texas
Permethrin, branded as Nix in North America, an anti-lice drug
"Nix", a song by Golden Boy with Miss Kittin from Or
The Nix, a 2017 novel by Nathan Hill
Neck (water spirit) or nix, an aquatic being in Germanic folklore

See also
All pages with titles beginning with Nix 
Nyx (disambiguation)
Nixe (disambiguation)
Nick (disambiguation)
NIC (disambiguation)
New York Knicks, basketball team