The square of total risk is the sum of the square of systematic risk and the square of specific risk. Specific risk is the standard deviation of the error term in the regression equation. Both terms are annualized to calculate total risk.
TotalRisk(Ra, Rb, Rf = 0, ...)$$Total Risk = \sqrt{Systematic Risk^2 + Specific Risk^2}$$
Carl Bacon, Practical portfolio performance measurement and attribution, second edition 2008 p.75
data(portfolio_bacon)
print(TotalRisk(portfolio_bacon[,1], portfolio_bacon[,2])) #expected 0.0134
#> [1] 0.136828
data(managers)
print(TotalRisk(managers['1996',1], managers['1996',8]))
#> [1] 0.05627721
print(TotalRisk(managers['1996',1:5], managers['1996',8]))
#> HAM1 HAM2 HAM3 HAM4 HAM5
#> Total Risk = 0.05627721 NA 0.1079938 0.1099375 NA