* A command `--switch-generation' to switch to a specific generation

  of the current profile, e.g.,

    $ nix-env --list-generations
    ...
    39   2004-02-02 17:53:53
    40   2004-02-02 17:55:18
    41   2004-02-02 17:55:41
    42   2004-02-02 17:55:50   (current)

    $ nix-env --switch-generation 39

    $ ls -l /nix/var/nix/profiles/default
    ... default -> default-39-link

* Also a command `--rollback' which is just a convenience operation to
  rollback to the oldest generation younger than the current one.

  Note that generations properly form a tree.  E.g., if after
  switching to generation 39, we perform an installation action,
  a generation 43 is created which is a descendant of 39, not 42.  So
  a rollback from 43 ought to go back to 39.  This is not currently
  implemented; generations form a linear sequence.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/nix-env/help.txt b/src/nix-env/help.txt
index 3832f1655b4e..9a772fc8330a 100644
--- a/src/nix-env/help.txt
+++ b/src/nix-env/help.txt
@@ -13,6 +13,10 @@ The previous operations take a list of derivation names.  The special
 name `*' may be used to indicate all derivations.
 
   --switch-profile / -S [FILE]: switch to specified profile
+  --switch-generation / -G NUMBER: switch to specified generation of profile
+  --rollback: switch to the previous generation
+  --list-generations: list available generations of a profile
+  
   --import / -I FILE: set default Nix expression
 
   --version: output version information