http://www.gromacs.org/Documentation/How-tos/Extending_Simulations

thanx

It says fatal error due to double command line argument -s

in gromacs you have md.mdp file, open that file and there is value name nsteps change that nstep value. 

like for 1 ns the value of nsteps is 1000 so for 2 ns the value would be 200 and for 100 ns it would become 100 x 1000.

just change the value and your simulation will run for 2 ns.

i hope this will help.

other wise whats app me.

No, kartikay I want to extend the simulation from 1ns to 2ns... Justin and thirumal are right... After changing the little bit of syntax it works for me...

Anyways thanx to all

i didn`t read justin`s comment, but u can change the simulation running time by changing the nstep value from md.mdp file and it will also work, i have done it by myself that why i suggested you to do that.