The assumptions of the classical linear regression model include:

1. Linear Parameter and correct model specification
2. Full Rank of Matrix
3. X Explanatory Variables must be exogenous
4. Independent and Identically Distributed Error Terms
5. Normal Distributed Error Terms in Population

Although the answers here provide already a good overview of the classical OLS assumption, you can find a more comprehensive description of the assumption of the classical linear regression model here:

https://economictheoryblog.com/2015/04/01/ols_assumptions/

In addition, the article describes the consequences in case one violates certain assumptions.

The assumptions of the classical linear regression model include:

1. Linear Parameter and correct model specification
2. Full Rank of the X Matrix
3. Explanatory Variables must be exogenous
4. Independent and Identically Distributed Error Terms
5. Normal Distributed Error Terms in Population

Although the answers here provide already a good overview of the classical OLS assumption, you can find a more comprehensive description of the assumption of the classical linear regression model here:

https://economictheoryblog.com/2015/04/01/ols_assumptions/

In addition, the article describes the consequences in case one violates certain assumptions.