restic/doc/Manual.md

nhanks for using restic. This document will give you an overview of the basic
functionality provided by restic.

# Installing restic

## from pre-compiled binary

You can download the latest pre-compiled binary from the [restic release page](https://github.com/restic/restic/releases/latest).

## Mac OS X

If you are using Mac OS X, you can install restic using the
[homebrew](http://brew.sh/) packet manager:

```console
$ brew tap restic/restic
$ brew install restic
```

## archlinux

On archlinux, there is a package called `restic-git` which can be installed from AUR, e.g. with `pacaur`:

```console
$ pacaur -S restic-git
```

# Building restic

restic is written in the Go programming language and you need at least Go version 1.7.
Building restic may also work with older versions of Go, but that's not supported.
See the [Getting started](https://golang.org/doc/install) guide of the Go project for
instructions how to install Go.

In order to build restic from source, execute the following steps:

```console
$ git clone https://github.com/restic/restic
[...]

$ cd restic

$ go run build.go
```

You can easily cross-compile restic for all supported platforms, just supply
the target OS and platform via the command-line options like this (for Windows
and FreeBSD respectively):

    $ go run build.go --goos windows --goarch amd64

    $ go run build.go --goos freebsd --goarch 386

The resulting binary is statically linked and does not require any libraries.

At the moment, the only tested compiler for restic is the official Go compiler.
Building restic with gccgo may work, but is not supported.

# Usage help

Usage help is available:

```console
$ ./restic --help
restic is a backup program which allows saving multiple revisions of files and
directories in an encrypted repository stored on different backends.

Usage:
  restic [command]

Available Commands:
  backup        create a new backup of files and/or directories
  cat           print internal objects to stdout
  check         check the repository for errors
  find          find a file or directory
  forget        forget removes snapshots from the repository
  init          initialize a new repository
  key           manage keys (passwords)
  list          list items in the repository
  ls            list files in a snapshot
  mount         mount the repository
  prune         remove unneeded data from the repository
  rebuild-index build a new index file
  restore       extract the data from a snapshot
  snapshots     list all snapshots
  tag           modifies tags on snapshots
  unlock        remove locks other processes created
  version       Print version information

Flags:
      --json                   set output mode to JSON for commands that support it
      --no-lock                do not lock the repo, this allows some operations on read-only repos
  -p, --password-file string   read the repository password from a file
  -q, --quiet                  do not output comprehensive progress report
  -r, --repo string            repository to backup to or restore from (default: $RESTIC_REPOSITORY)

Use "restic [command] --help" for more information about a command.
```

Similar to programs such as `git`, restic has a number of sub-commands. You can
see these commands in the listing above. Each sub-command may have own
command-line options, and there is a help option for each command which lists
them, e.g. for the `backup` command:

```console
$ ./restic backup --help
The "backup" command creates a new snapshot and saves the files and directories
given as the arguments.

Usage:
  restic backup [flags] FILE/DIR [FILE/DIR] ...

Flags:
  -e, --exclude pattern         exclude a pattern (can be specified multiple times)
      --exclude-file string     read exclude patterns from a file
      --files-from string       read the files to backup from file (can be combined with file args)
  -f, --force                   force re-reading the target files/directories. Overrides the "parent" flag
  -x, --one-file-system         Exclude other file systems
      --parent string           use this parent snapshot (default: last snapshot in the repo that has the same target files/directories)
      --stdin                   read backup from stdin
      --stdin-filename string   file name to use when reading from stdin
      --tag tag                 add a tag for the new snapshot (can be specified multiple times)

Global Flags:
      --json                   set output mode to JSON for commands that support it
      --no-lock                do not lock the repo, this allows some operations on read-only repos
  -p, --password-file string   read the repository password from a file
  -q, --quiet                  do not output comprehensive progress report
  -r, --repo string            repository to backup to or restore from (default: $RESTIC_REPOSITORY)
```

Subcommand that support showing progress information such as `backup`, `check` and `prune` will do so unless
the quiet flag `-q` or `--quiet` is set. When running from a non-interactive console progress reporting will
be limited to once every 10 seconds to not fill your logs.

Additionally on Unix systems if `restic` receives a SIGUSR signal the current progress will written to the
standard output so you can check up on the status at will.


# Initialize a repository

First, we need to create a "repository". This is the place where your backups
will be saved at.

In order to create a repository at `/tmp/backup`, run the following command and
enter the same password twice:

```console
$ restic init --repo /tmp/backup
enter password for new backend:
enter password again:
created restic backend 085b3c76b9 at /tmp/backup
Please note that knowledge of your password is required to access the repository.
Losing your password means that your data is irrecoverably lost.
```

Other backends like sftp and s3 are [described in a later section](#create-an-sftp-repository) of this document.

Remembering your password is important! If you lose it, you won't be able to
access data stored in the repository.

For automated backups, restic accepts the repository location in the
environment variable `RESTIC_REPOSITORY`. The password can be read from a file
(via the option `--password-file`) or the environment variable
`RESTIC_PASSWORD`.

## Password prompt on Windows

At the moment, restic only supports the default Windows console interaction.
If you use emulation environments like [MSYS2](https://msys2.github.io/) or
[Cygwin](https://www.cygwin.com/), which use terminals like `Mintty` or `rxvt`,
you may get a password error:

You can workaround this by using a special tool called `winpty` (look
[here](https://sourceforge.net/p/msys2/wiki/Porting/) and
[here](https://github.com/rprichard/winpty) for detail information). On MSYS2,
you can install `winpty` as follows:

```console
$ pacman -S winpty
$ winpty restic -r /tmp/backup init
```

# Create a snapshot

Now we're ready to backup some data. The contents of a directory at a specific
point in time is called a "snapshot" in restic. Run the following command and
enter the repository password you chose above again:

```console
$ restic -r /tmp/backup backup ~/work
enter password for repository:
scan [/home/user/work]
scanned 764 directories, 1816 files in 0:00
[0:29] 100.00%  54.732 MiB/s  1.582 GiB / 1.582 GiB  2580 / 2580 items  0 errors  ETA 0:00
duration: 0:29, 54.47MiB/s
snapshot 40dc1520 saved
```

As you can see, restic created a backup of the directory and was pretty fast!
The specific snapshot just created is identified by a sequence of hexadecimal
characters, `40dc1520` in this case.

If you run the command again, restic will create another snapshot of your data,
but this time it's even faster. This is de-duplication at work!

```console
$ restic -r /tmp/backup backup ~/shared/work/web
enter password for repository:
using parent snapshot 40dc1520aa6a07b7b3ae561786770a01951245d2367241e71e9485f18ae8228c
scan [/home/user/work]
scanned 764 directories, 1816 files in 0:00
[0:00] 100.00%  0B/s  1.582 GiB / 1.582 GiB  2580 / 2580 items  0 errors  ETA 0:00
duration: 0:00, 6572.38MiB/s
snapshot 79766175 saved
```

You can even backup individual files in the same repository.

```console
$ restic -r /tmp/backup backup ~/work.txt
scan [~/work.txt]
scanned 0 directories, 1 files in 0:00
[0:00] 100.00%  0B/s  220B / 220B  1 / 1 items  0 errors  ETA 0:00
duration: 0:00, 0.03MiB/s
snapshot 31f7bd63 saved
```

In fact several hosts may use the same repository to backup directories and
files leading to a greater de-duplication.

Please be aware that when you backup different directories (or the directories
to be saved have a variable name component like a time/date), restic always
needs to read all files and only afterwards can compute which parts of the
files need to be saved. When you backup the same directory again (maybe with
new or changed files) restic will find the old snapshot in the repo and by
default only reads those files that are new or have been modified since the
last snapshot. This is decided based on the modify date of the file in the
file system.

You can exclude folders and files by specifying exclude-patterns.
Either specify them with multiple `--exclude`'s or one `--exclude-file`

```console
$ cat exclude
# exclude go-files
*.go
# exclude foo/x/y/z/bar foo/x/bar foo/bar
foo/**/bar
$ restic -r /tmp/backup backup ~/work --exclude=*.c --exclude-file=exclude
```

Patterns use [`filepath.Glob`](https://golang.org/pkg/path/filepath/#Glob) internally,
see [`filepath.Match`](https://golang.org/pkg/path/filepath/#Match) for syntax.
Additionally `**` excludes arbitrary subdirectories.
Environment-variables in exclude-files are expanded with [`os.ExpandEnv`](https://golang.org/pkg/os/#ExpandEnv).

By specifying the option `--one-file-system` you can instruct restic to only
backup files from the file systems the initially specified files or directories
reside on. For example, calling restic like this won't backup `/sys` or
`/dev` on a Linux system:

```console
$ restic -r /tmp/backup backup --one-file-system /
```
By using the `--files-from` option you can read the files you want to backup
from a file. This is especially useful if a lot of files have to be backed up
that are not in the same folder or are maybe pre-filtered by other software.

For example maybe you want to backup files that have a certain filename in them:

```console
$ find /tmp/somefiles | grep 'PATTERN' > /tmp/files_to_backup
```

You can then use restic to backup the filtered files:

```console
$ restic -r /tmp/backup backup --files-from /tmp/files_to_backup
```

Incidentally you can also combine `--files-from` with the normal files args:

```console
$ restic -r /tmp/backup backup --files-from /tmp/files_to_backup /tmp/some_additional_file
```

## Reading data from stdin

Sometimes it can be nice to directly save the output of a program, e.g.
`mysqldump` so that the SQL can later be restored. Restic supports this mode of
operation, just supply the option `--stdin` to the `backup` command like this:

```console
$ mysqldump [...] | restic -r /tmp/backup backup --stdin
```

This creates a new snapshot of the output of `mysqldump`. You can then use e.g.
the fuse mounting option (see below) to mount the repository and read the file.

By default, the file name `stdin` is used, a different name can be specified
with `--stdin-filename`, e.g. like this:

```console
$ mysqldump [...] | restic -r /tmp/backup backup --stdin --stdin-filename production.sql
```

## Tags

Snapshots can have one or more tags, short strings which add identifying
information. Just specify the tags for a snapshot with `--tag`:

```console
$ restic -r /tmp/backup backup --tag projectX ~/shared/work/web
[...]
```

The tags can later be used to keep (or forget) snapshots.

# List all snapshots

Now, you can list all the snapshots stored in the repository:

```console
$ restic -r /tmp/backup snapshots
enter password for repository:
ID        Date                 Host    Tags   Directory
----------------------------------------------------------------------
40dc1520  2015-05-08 21:38:30  kasimir        /home/user/work
79766175  2015-05-08 21:40:19  kasimir        /home/user/work
bdbd3439  2015-05-08 21:45:17  luigi          /home/art
590c8fc8  2015-05-08 21:47:38  kazik          /srv
9f0bc19e  2015-05-08 21:46:11  luigi          /srv
```

You can filter the listing by directory path:

```console
$ restic -r /tmp/backup snapshots --path="/srv"
enter password for repository:
ID        Date                 Host    Tags   Directory
----------------------------------------------------------------------
590c8fc8  2015-05-08 21:47:38  kazik          /srv
9f0bc19e  2015-05-08 21:46:11  luigi          /srv
```

Or filter by host:

```console
$ restic -r /tmp/backup snapshots --host luigi
enter password for repository:
ID        Date                 Host    Tags   Directory
----------------------------------------------------------------------
bdbd3439  2015-05-08 21:45:17  luigi          /home/art
9f0bc19e  2015-05-08 21:46:11  luigi          /srv
```

Combining filters is also possible.

# Restore a snapshot

Restoring a snapshot is as easy as it sounds, just use the following command to
restore the contents of the latest snapshot to `/tmp/restore-work`:

```console
$ restic -r /tmp/backup restore 79766175 --target ~/tmp/restore-work
enter password for repository:
restoring <Snapshot of [/home/user/work] at 2015-05-08 21:40:19.884408621 +0200 CEST> to /tmp/restore-work
```

Use the word `latest` to restore the last backup. You can also combine `latest`
with the `--host` and `--path` filters to choose the last backup for a specific
host, path or both.

```console
$ restic -r /tmp/backup restore latest --target ~/tmp/restore-work --path "/home/art" --host luigi
enter password for repository:
restoring <Snapshot of [/home/art] at 2015-05-08 21:45:17.884408621 +0200 CEST> to /tmp/restore-work
```

# Manage repository keys

The `key` command allows you to set multiple access keys or passwords per
repository. In fact, you can use the `list`, `add`, `remove` and `passwd`
sub-commands to manage these keys very precisely:

```console
$ restic -r /tmp/backup key list
enter password for repository:
 ID          User        Host        Created
----------------------------------------------------------------------
*eb78040b    username    kasimir   2015-08-12 13:29:57

$ restic -r /tmp/backup key add
enter password for repository:
enter password for new key:
enter password again:
saved new key as <Key of username@kasimir, created on 2015-08-12 13:35:05.316831933 +0200 CEST>

$ restic -r backup key list
enter password for repository:
 ID          User        Host        Created
----------------------------------------------------------------------
 5c657874    username    kasimir   2015-08-12 13:35:05
*eb78040b    username    kasimir   2015-08-12 13:29:57
```

# Manage tags

Managing tags on snapshots is done with the `tag` command. The existing set of
tags can be replaced completely, tags can be added to removed. The result is
directly visible in the `snapshots` command.

Let's say we want to tag snapshot `590c8fc8` with the tags `NL` and `CH` and
remove all other tags that may be present, the following command does that:

```console
$ restic -r /tmp/backup tag --set NL,CH 590c8fc8
Create exclusive lock for repository
Modified tags on 1 snapshots
```

Note the snapshot ID has changed, so between each change we need to look up
the new ID of the snapshot. But there is an even better way, the `tag` command
accepts `--tag` for a filter, so we can filter snapshots based on the tag we
just added.

So we can add and remove tags incrementally like this:

```console
$ restic -r /tmp/backup tag --tag NL --remove CH
Create exclusive lock for repository
Modified tags on 1 snapshots

$ restic -r /tmp/backup tag --tag NL --add UK
Create exclusive lock for repository
Modified tags on 1 snapshots

$ restic -r /tmp/backup tag --tag NL --remove NL
Create exclusive lock for repository
Modified tags on 1 snapshots

$ restic -r /tmp/backup tag --tag NL --add SOMETHING
No snapshots were modified
```

# Check integrity and consistency

Imagine your repository is saved on a server that has a faulty hard drive, or
even worse, attackers get privileged access and modify your backup with the
intention to make you restore malicious data:

```console
$ sudo echo "boom" >> backup/index/d795ffa99a8ab8f8e42cec1f814df4e48b8f49129360fb57613df93739faee97
```

In order to detect these things, it is a good idea to regularly use the `check`
command to test whether everything is alright, your precious backup data is
consistent and the integrity is unharmed:

```console
$ restic -r /tmp/backup check
Load indexes
ciphertext verification failed
```

Trying to restore a snapshot which has been modified as shown above will yield
the same error:

```console
$ restic -r /tmp/backup restore 79766175 --target ~/tmp/restore-work
Load indexes
ciphertext verification failed
```

# Mount a repository

Browsing your backup as a regular file system is also very easy. First, create
a mount point such as `/mnt/restic` and then use the following command to serve
the repository with FUSE:

```console
$ mkdir /mnt/restic
$ restic -r /tmp/backup mount /mnt/restic
enter password for repository:
Now serving /tmp/backup at /tmp/restic
Don't forget to umount after quitting!
```

Mounting repositories via FUSE is not possible on Windows and OpenBSD.

Restic supports storage and preservation of hard links. However, since hard links
exist in the scope of a filesystem by definition, restoring hard links from a fuse
mount should be done by a program that preserves hard links. A program that does so
is rsync, used with the option --hard-links.

# Create an SFTP repository

In order to backup data via SFTP, you must first set up a server with SSH and
let it know your public key. Passwordless login is really important since
restic fails to connect to the repository if the server prompts for
credentials.

Once the server is configured, the setup of the SFTP repository can simply be
achieved by changing the URL scheme in the `init` command:

```console
$ restic -r sftp:user@host:/tmp/backup init
enter password for new backend:
enter password again:
created restic backend f1c6108821 at sftp:user@host:/tmp/backup
Please note that knowledge of your password is required to access the repository.
Losing your password means that your data is irrecoverably lost.
```

You can also specify a relative (read: no slash (`/`) character at the
beginning) directory, in this case the dir is relative to the remote user's
home directory.

The backend config string does not allow specifying a port. If you need to
contact an sftp server on a different port, you can create an entry in the
`ssh` file, usually located in your user's home directory at `~/.ssh/config` or
in `/etc/ssh/ssh_config`:

```
Host foo
    User bar
    Port 2222
```

Then use the specified host name `foo` normally (you don't need to specify the
user name in this case):

```
$ restic -r sftp:foo:/tmp/backup init
```

You can also add an entry with a special host name which does not exist, just
for use with restic, and use the `Hostname` option to set the real host name:

```
Host restic-backup-host
    Hostname foo
    User bar
    Port 2222
```

Then use it in the backend specification:

```
$ restic -r sftp:restic-backup-host:/tmp/backup init
```

Last, if you'd like to use an entirely different program to create the SFTP
connection, you can specify the command to be run with the option
`-o sftp.command="foobar"`.

# Create a REST server repository

In order to backup data to the remote server via HTTP or HTTPS protocol,
you must first set up a remote [REST server](https://github.com/restic/rest-server)
instance.  Once the server is configured, accessing it is achieved by changing the
URL scheme like this:

```console
$ restic -r rest:http://host:8000/
```

Depending on your REST server setup, you can use HTTPS protocol, password
protection, or multiple repositories.  Or any combination of those features, as
you see fit. TCP/IP port is also configurable. Here are some more examples:

```console
$ restic -r rest:https://host:8000/
$ restic -r rest:https://user:pass@host:8000/
$ restic -r rest:https://user:pass@host:8000/my_backup_repo/
```

If you use TLS, make sure your certificates are signed, 'cause restic client
will refuse to communicate otherwise.  It's easy to obtain such certificates
today, thanks to free certificate authorities like [Let’s
Encrypt](https://letsencrypt.org/).

REST server uses exactly the same directory structure as local backend, so you
should be able to access it both locally and via HTTP, even simultaneously.

# Create an Amazon S3 repository

Restic can backup data to any Amazon S3 bucket. However, in this case, changing the URL scheme is not enough since Amazon uses special security credentials to sign HTTP requests. By consequence, you must first setup the following environment variables with the credentials you obtained while creating the bucket.

```console
$ export AWS_ACCESS_KEY_ID=<MY_ACCESS_KEY>
$ export AWS_SECRET_ACCESS_KEY=<MY_SECRET_ACCESS_KEY>
```

You can then easily initialize a repository that uses your Amazon S3 as a backend, if the bucket does not exist yet it will be created in the default location:

```console
$ restic -r s3:s3.amazonaws.com/bucket_name init
enter password for new backend:
enter password again:
created restic backend eefee03bbd at s3:s3.amazonaws.com/bucket_name
Please note that knowledge of your password is required to access the repository.
Losing your password means that your data is irrecoverably lost.
```

It is not possible at the moment to have restic create a new bucket in a different location, so you need to create it using a different program. Afterwards, the S3 server (`s3.amazonaws.com`) will redirect restic to the correct endpoint.

For an S3-compatible server that is not Amazon (like Minio, see below), or is
only available via HTTP, you can specify the URL to the server like this:
`s3:http://server:port/bucket_name`.

## Create a Minio Server repository

[Minio](https://www.minio.io) is an Open Source Object Storage, written in Go and compatible with AWS S3 API.

### Pre-Requisites

* Download and Install [Minio Server](https://minio.io/downloads/#minio-server).
* You can also refer to [https://docs.minio.io](https://docs.minio.io) for step by step guidance on installation and getting started on Minio Client and Minio Server.

You must first setup the following environment variables with the credentials of your running Minio Server.

```console
$ export AWS_ACCESS_KEY_ID=<YOUR-MINIO-ACCESS-KEY-ID>
$ export AWS_SECRET_ACCESS_KEY= <YOUR-MINIO-SECRET-ACCESS-KEY>
```

Now you can easily initialize restic to use Minio server as backend with this command.

```console
$ ./restic -r s3:http://localhost:9000/restic init
enter password for new backend:
enter password again:
created restic backend 6ad29560f5 at s3:http://localhost:9000/restic1
Please note that knowledge of your password is required to access
the repository. Losing your password means that your data is irrecoverably lost.
```

# Removing old snapshots

All backup space is finite, so restic allows removing old snapshots. This can
be done either manually (by specifying a snapshot ID to remove) or by using a
policy that describes which snapshots to forget. For all remove operations, two
commands need to be called in sequence: `forget` to remove a snapshot and
`prune` to actually remove the data that was referenced by the snapshot from
the repository. This can be automated with the `--prune` option of the `forget`
command, which runs `prune` automatically if snapshots have been removed.

## Remove a single snapshot

The command `snapshots` can be used to list all snapshots in a repository like this:

```console
$ restic -r /tmp/backup snapshots
enter password for repository:
ID        Date                 Host      Tags  Directory
----------------------------------------------------------------------
40dc1520  2015-05-08 21:38:30  kasimir         /home/user/work
79766175  2015-05-08 21:40:19  kasimir         /home/user/work
bdbd3439  2015-05-08 21:45:17  luigi           /home/art
590c8fc8  2015-05-08 21:47:38  kazik           /srv
9f0bc19e  2015-05-08 21:46:11  luigi           /srv
```

In order to remove the snapshot of `/home/art`, use the `forget` command and
specify the snapshot ID on the command line:

```console
$ restic -r /tmp/backup forget bdbd3439
enter password for repository:
removed snapshot d3f01f63
```

Afterwards this snapshot is removed:

```console
$ restic -r /tmp/backup snapshots
enter password for repository:
ID        Date                 Host     Tags  Directory
----------------------------------------------------------------------
40dc1520  2015-05-08 21:38:30  kasimir        /home/user/work
79766175  2015-05-08 21:40:19  kasimir        /home/user/work
590c8fc8  2015-05-08 21:47:38  kazik          /srv
9f0bc19e  2015-05-08 21:46:11  luigi          /srv
```

But the data that was referenced by files in this snapshot is still stored in
the repository. To cleanup unreferenced data, the `prune` command must be run:

```console
$ restic -r /tmp/backup prune
enter password for repository:

counting files in repo
building new index for repo
[0:00] 100.00%  22 / 22 files
repository contains 22 packs (8512 blobs) with 100.092 MiB bytes
processed 8512 blobs: 0 duplicate blobs, 0B duplicate
load all snapshots
find data that is still in use for 1 snapshots
[0:00] 100.00%  1 / 1 snapshots
found 8433 of 8512 data blobs still in use
will rewrite 3 packs
creating new index
[0:00] 86.36%  19 / 22 files
saved new index as 544a5084
done
```

Afterwards the repository is smaller.

You can automate this two-step process by using the `--prune` switch to
`forget`:

```console
$ restic forget --keep-last 1 --prune
snapshots for host mopped, directories /home/user/work:

keep 1 snapshots:
ID        Date                 Host        Tags        Directory
----------------------------------------------------------------------
4bba301e  2017-02-21 10:49:18  mopped                  /home/user/work

remove 1 snapshots:
ID        Date                 Host        Tags        Directory
----------------------------------------------------------------------
8c02b94b  2017-02-21 10:48:33  mopped                  /home/user/work

1 snapshots have been removed, running prune
counting files in repo
building new index for repo
[0:00] 100.00%  37 / 37 packs
repository contains 37 packs (5521 blobs) with 151.012 MiB bytes
processed 5521 blobs: 0 duplicate blobs, 0B duplicate
load all snapshots
find data that is still in use for 1 snapshots
[0:00] 100.00%  1 / 1 snapshots
found 5323 of 5521 data blobs still in use, removing 198 blobs
will delete 0 packs and rewrite 27 packs, this frees 22.106 MiB
creating new index
[0:00] 100.00%  30 / 30 packs
saved new index as b49f3e68
done
```


## Removing snapshots according to a policy

Removing snapshots manually is tedious and error-prone, therefore restic allows
specifying which snapshots should be removed automatically according to a
policy. You can specify how many hourly, daily, weekly, monthly and yearly
snapshots to keep, any other snapshots are removed. The most important
command-line parameter here is `--dry-run` which instructs restic to not remove
anything but print which snapshots would be removed.

When `forget` is run with a policy, restic loads the list of all snapshots,
then groups these by host name and list of directories. The policy is then
applied to each group of snapshots separately. This is a safety feature.

The `forget` command accepts the following parameters:

 * `--keep-last n` never delete the `n` last (most recent) snapshots
 * `--keep-hourly n` for the last `n` hours in which a snapshot was made, keep
   only the last snapshot for each hour.
 * `--keep-daily n` for the last `n` days which have one or more snapshots, only
   keep the last one for that day.
 * `--keep-weekly n` for the last `n` weeks which have one or more snapshots, only
   keep the last one for that week.
 * `--keep-monthly n` for the last `n` months which have one or more snapshots, only
   keep the last one for that month.
 * `--keep-yearly n` for the last `n` years which have one or more snapshots, only
   keep the last one for that year.
 * `--keep-tag` keep all snapshots which have all tags specified by this option
   (can be specified multiple times).

Additionally, you can restrict removing snapshots to those which have a
particular hostname with the `--hostname` parameter, or tags with the `--tag`
option. When multiple tags are specified, only the snapshots which have all the
tags are considered.

All the `--keep-*` options above only count hours/days/weeks/months/years which
have a snapshot, so those without a snapshot are ignored.

Let's explain this with an example: Suppose you have only made a backup on each
Sunday for 12 weeks. Then `forget --keep-daily 4` will keep the last four snapshots
for the last four Sundays, but remove the rest. Only counting the days which
have a backup and ignore the ones without is a safety feature: it prevents
restic from removing many snapshots when no new ones are created. If it was
implemented otherwise, running `forget --keep-daily 4` on a Friday would remove
all snapshots!

# Debugging restic

The program can be built with debug support like this:

```console
$ go run build.go -tags debug
```

Afterwards, extensive debug messages are written to the file in environment
variable `DEBUG_LOG`, e.g.:

```console
$ DEBUG_LOG=/tmp/restic-debug.log restic backup ~/work
```

If you suspect that there is a bug, you can have a look at the debug log.
Please be aware that the debug log might contain sensitive information such as
file and directory names.

The debug log will always contain all log messages restic generates. You can
also instruct restic to print some or all debug messages to stderr. These can
also be limited to e.g. a list of source files or a list of patterns for
function names. The patterns are globbing patterns (see the documentation for
[`path.Glob`](https://golang.org/pkg/path/#Glob)), multiple patterns are
separated by commas. Patterns are case sensitive.

Printing all log messages to the console can be achieved by setting the file
filter to `*`:

```console
$ DEBUG_FILES=* restic check
```

If you want restic to just print all debug log messages from the files
`main.go` and `lock.go`, set the environment variable `DEBUG_FILES` like this:

```console
$ DEBUG_FILES=main.go,lock.go restic check
```

The following command line instructs restic to only print debug statements
originating in functions that match the pattern `*unlock*` (case sensitive):

```console
$ DEBUG_FUNCS=*unlock* restic check
```

# Under the hood: Browse repository objects

Internally, a repository stores data of several different types described in the [design documentation](https://github.com/restic/restic/blob/master/doc/Design.md). You can `list` objects such as blobs, packs, index, snapshots, keys or locks with the following command:

```console
$ restic -r /tmp/backup list snapshots
d369ccc7d126594950bf74f0a348d5d98d9e99f3215082eb69bf02dc9b3e464c
```

The `find` command searches for a given
[pattern](http://golang.org/pkg/path/filepath/#Match) in the repository.

```console
$ restic -r backup find test.txt
debug log file restic.log
debug enabled
enter password for repository:
found 1 matching entries in snapshot 196bc5760c909a7681647949e80e5448e276521489558525680acf1bd428af36
  -rw-r--r--   501    20      5 2015-08-26 14:09:57 +0200 CEST path/to/test.txt
```

The `cat` command allows you to display the JSON representation of the objects
or its raw content.

```console
$ restic -r /tmp/backup cat snapshot d369ccc7d126594950bf74f0a348d5d98d9e99f3215082eb69bf02dc9b3e464c
enter password for repository:
{
  "time": "2015-08-12T12:52:44.091448856+02:00",
  "tree": "05cec17e8d3349f402576d02576a2971fc0d9f9776ce2f441c7010849c4ff5af",
  "paths": [
    "/home/user/work"
  ],
  "hostname": "kasimir",
  "username": "username",
  "uid": 501,
  "gid": 20
}
```

# Scripting restic

Restic supports the output of some commands in JSON format, the JSON data can
then be processed by other programs (e.g. [`jq`](https://stedolan.github.io/jq/)).
The following example lists all snapshots as JSON and uses `jq` to pretty-print
the result:

```console
$ restic -r /tmp/backup snapshots --json | jq .
[
  {
    "time": "2017-03-11T09:57:43.26630619+01:00",
    "tree": "bf25241679533df554fc0fd0ae6dbb9dcf1859a13f2bc9dd4543c354eff6c464",
    "paths": [
      "/home/work/doc"
    ],
    "hostname": "kasimir",
    "username": "fd0",
    "uid": 1000,
    "gid": 100,
    "id": "bbeed6d28159aa384d1ccc6fa0b540644b1b9599b162d2972acda86b1b80f89e"
  },
  {
    "time": "2017-03-11T09:58:57.541446938+01:00",
    "tree": "7f8c95d3420baaac28dc51609796ae0e0ecfb4862b609a9f38ffaf7ae2d758da",
    "paths": [
      "/home/user/shared"
    ],
    "hostname": "kasimir",
    "username": "fd0",
    "uid": 1000,
    "gid": 100,
    "id": "b157d91c16f0ba56801ece3a708dfc53791fe2a97e827090d6ed9a69a6ebdca0"
  }
]
```

# Temporary files

During some operations (e.g. `backup` and `prune`) restic uses temporary files
to store data. These files will, by default, be saved to the system's temporary
directory, on Linux this is usually located in `/tmp/`. The environment
variable `TMPDIR` can be used to specify a different directory, e.g. to use the
directory `/var/tmp/restic-tmp` instead of the default, set the environment
variable like this:

```console
$ export TMPDIR=/var/tmp/restic-tmp
$ restic -r /tmp/backup backup ~/work
```