I am highly frustrated by the behaviour of the standard unix sort command, which seems to always sort on all fields of a line, even if I specify one field to sort on.

If input of sort is like:
ON user2
OFF user2
ON user1

'cat input | sort +1' will always produce the following output:
ON user1
OFF user2
ON user2

Note that the output is also sorted on field0, though noone told sort to sort on field0.
Is there a way to tell sort not to sort on a specific field, i.e. leaving the lines in the positional order, instead?

My intention is that the sort output should be like this:
ON user1
ON user2
OFF user2
(i.e. it is not sorted on field0, only on field1)

man sort says:

-s stabilize sort by disabling last resort comparison

cat infile.sort
ON user2
OFF user2
ON user1

$ sort -s +1 infile.sort
ON user1
ON user2
OFF user2

try sort -k 2,2

-k specifies the key field to sort on. The n,m argument specify the first and the last fields to sort on.

Thank you for the tips, both worked.
I already tried out a sort -k command, which (now I know) did not work as I thought the first data is field 0, the second is field 1, so tried sort -k 1,1 and dropped the idea when it did not work.