3 Nsscash (a pun on cache) is a simple file-based cache for NSS similar to
4 nsscache [1]. The goal is to distribute users/groups/etc. to multiple systems
5 without having to rely on a (single) stable server. Traditional systems like
6 LDAP or NIS require a stable server or users/groups cannot be resolved. By
7 distributing the data to all systems, temporary outages of the server cause no
8 issues on the clients. In addition the local storage is much faster than
9 remote network access. To update the local caches polling via HTTP is
10 performed, for example every minute, only downloading new data if anything has
13 Nsscash consists of two parts: `nsscash`, written in Go, which downloads files
14 via HTTP or HTTPS, parses them, creates indices and writes the result to a
15 local file. The second part is the NSS module (`libnss_cash.so.2`), written in
16 C, which provides integration via `/etc/nsswitch.conf`. It's specifically
17 designed to be very simple and uses the data prepared by `nsscash` for
18 lookups. To support quick lookups, in O(log n), the files utilize indices.
20 Nsscash is very careful when deploying the changes:
21 - All files are updated using the standard "write to temporary file", "sync",
22 "rename" steps which is atomic on UNIX file systems.
23 - All errors cause an immediate abort ("fail fast") with a proper error
24 message and a non-zero exit status. This prevents hiding possibly important
25 errors. In addition all files are fetched first and then deployed to try to
26 prevent inconsistent state if only one file can be downloaded. The state
27 file (containing last file modifications) is only updated when all
28 operations were successful.
29 - To prevent unexpected permissions, `nsscash` does not create new files. The
30 user must create them first and `nsscash` will then re-use the permissions
31 and owner/group when updating the file (see examples below).
32 - To prevent misconfigurations, empty files (no users/groups) are not
33 permitted and will not be written to disk. This is designed to prevent the
34 accidental loss of all users/groups on a system.
36 The passwd/group files have the following size restrictions:
37 - maximum number of entries: '2^64-1' (uint64_t)
38 - maximum passwd entry size: 65543 bytes (including newline)
39 - maximum group entry size: 65535 bytes (including newline, only one member)
40 - maximum members per group: depends on the user name length,
41 with 9 bytes per user: 5460 users
42 - `nsscash` checks for these restrictions and aborts with an error if they are
45 nsscash is licensed under AGPL version 3 or later.
47 [1] https://github.com/google/nsscache
53 - github.com/pkg/errors
54 - github.com/BurntSushi/toml
55 - C compiler, for `libnss_cash.so.2`
57 Tested on Debian Stretch and Buster, but should work on any GNU/Linux system.
58 With adapations to the NSS module it should work on any UNIX-like system which
64 Install `libnss_cash.so.2` somewhere in your library search path (see
65 `/etc/ld.so.conf`), e.g. `/usr/lib/x86_64-linux-gnu/`.
67 Update `/etc/nsswitch.conf` to include the cash module; `passwd` and `group`
68 are currently supported. For example:
74 Create the cache files with the proper permissions (`nsscash fetch` won't
75 create new files to prevent using incorrect permissions):
77 touch /etc/passwd.nsscash
78 touch /etc/group.nsscash
79 chmod 0644 /etc/passwd.nsscash
80 chmod 0644 /etc/group.nsscash
82 Configure the `nsscash` configuration file `nsscash.toml`, see below.
86 nsscash fetch /path/to/config/nsscash.toml
88 This will fetch the configured files and update the local caches. The files
89 are atomically overwritten (via temporary file, sync, and rename).
91 Verify the users/groups are available, e.g. with `getent`. If everything
92 works, remember to reboot the host as changes to `nsswitch.conf` don't affect
95 Now configure `nsscash` to run regularly, for example via cron or a systemd
100 Nsscash is configured through a simple configuration file written in TOML. A
101 typical configuration looks like this:
103 statepath = "/var/lib/nsscash/state.json"
107 url = "https://example.org/passwd"
108 path = "/etc/passwd.nsscash"
112 url = "https://example.org/group"
113 path = "/etc/group.nsscash"
115 # Optional, but useful to deploy files which are not supported by the
116 # nsscash NSS module, but by libc's "files" NSS module. nsscash takes care
117 # of the atomic replacement and updates; an "netgroup: files" entry in
118 # "/etc/nsswitch.conf" makes the netgroups available.
121 url = "https://example.org/netgroup"
122 path = "/etc/netgroup"
124 The following global keys are available:
126 - `statepath`: Path to a JSON file which stores the last modification time of
127 each file; automatically updated by `nsscash`. Used to fetch data only when
128 something has changed to reduce the required traffic.
130 Each `file` block describes a single file to download/write. The following
133 - `type`: Type of this file; can be either `passwd` (for files in
134 `/etc/passwd` format), `group` (for files in `/etc/group` format), or
135 `plain` (arbitrary format). Only `passwd` and `group` files are supported by
136 the nsscash NSS module. But, as explained above, `plain` can be used to
137 distribute arbitrary files. The type is required as the `.nsscash` files are
138 pre processed for faster lookups and simpler code which requires a known
141 - `url`: URL to fetch the file from; HTTP and HTTPS are supported
143 - `path`: Path to store the retrieved file
148 Written by Simon Ruderich <simon@ruderich.org>.
153 This program is licensed under AGPL version 3 or later.
155 Copyright (C) 2019 Simon Ruderich
157 This program is free software: you can redistribute it and/or modify
158 it under the terms of the GNU Affero General Public License as published by
159 the Free Software Foundation, either version 3 of the License, or
160 (at your option) any later version.
162 This program is distributed in the hope that it will be useful,
163 but WITHOUT ANY WARRANTY; without even the implied warranty of
164 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
165 GNU Affero General Public License for more details.
167 You should have received a copy of the GNU Affero General Public License
168 along with this program. If not, see <https://www.gnu.org/licenses/>.