AIX

#! /bin/nawk -f
#
# formatDF.nawk 
#

{

           for(i=0;i<=NF;i++){
                     lineArray[NR,i] = $i
                     if ( NF > numFields ) numFields = NF
                     if ( length($i) > lineLength[i] ) lineLength[i] = length($i)
           }
}
END{
           for(x=1;x<=NR;x++){
                if ( x == 1 ){
                     for(y=1;y<numFields-1;y++){
                               printf("%-"lineLength[y]"s ", lineArray[x,y])
                        }
                        printf("%s %s\n", lineArray[x,numFields -1], lineArray[x,numFields])
                }
                else {
                for(y=1;y<=numFields;y++){
                          printf("%-"lineLength[y]"s ", lineArray[x,y])
                }
                printf("\n")
                }
           }
}

df -k | formatDF.nawk