Rsync cronjob, который будет работать, только если rsync еще не запущен

Рекурсивный подход:

# V is the target value, t is the tolerance
# A is the list of values
# B is the subset of A that is still below V-t
def combination_in_range(V, t, A, B=[]):
    for i,a in enumerate(A):
        if a > V+t:    # B+[a] is too large
            continue

        # B+[a] can still be a possible list
        B.append(a)

        if a >= V-t:   # Found a set that works
            print B

        # recursively try with a reduced V
        # and a shortened list A
        combination_in_range(V-a, t, A[i+1:], B)

        B.pop()        # drop [a] from possible list

A=[0.4, 2, 3, 1.4, 2.6, 6.3]
combination_in_range(5, 0.5, A)