The distributions of ions enclosed in a charged cylindrical capillary with impenetrable surfaces are studied by using (i) the Poisson-Boltzmann theory, (ii) the modified Poisson-Boltzmann theory, and (iii) the Monte Carlo method. The ions are treated in the primitive model approximation, while the inner surface of the capillary is taken to have a uniform charge density. The results for the wall-ion distributions are presented for the capillary containing mono- or divalent counterions and size symmetric 1:1 or 2:2 electrolytes. Some calculations for the mean activity coefficients of the added electrolytes are also reported. The Monte Carlo results for the concentration profiles and the electrolyte activities are used to asses the validity of the potential theories. The modified Poisson-Boltzmann theory is found to be in good agreement with the simulation results for both mono- and divalent ions present in the solution. As expected, the regular Poisson-Boltzmann theory provides reasonable descriptions of solutions containing monovalent ions but fares relatively poorly in describing systems where divalent ions are present.