University librarians sign for three years depending on the specific regulations and policies of the university. Establishment refers to an administrative system in which public officials are granted specific grades and positions according to certain procedures and conditions under the civil service system. Generally speaking, university librarians belong to public institutions, not directly to the establishment of civil servants.

However, there may be some differences in the post setting and employment methods of different universities. Some universities may offer the position of librarian, that is to say, they need to go through examination, interview and other procedures to meet certain conditions before granting the position. In this case, the librarian who has signed a contract for three years may have the establishment.

To answer this question accurately, I suggest you consult the relevant regulations of your university, or consult the human resources department to get a specific answer.