update for modern installer layout and talk about hammer2

[ikiwiki.git] / docs / handbook / environmentquickstart / index.mdwn

# DragonFly BSD Quick Start

This document describes the DragonFly environment one will find on a newly installed system.  While you are getting started, please pay careful attention to the version or level of DragonFly that the documentation was written for.

[[!toc levels=3]]

## Some Unix and BSD Fundamentals

If you have used another Unix flavor before, you may need to spend some time learning the differences between DragonFly and the system you are experienced in.  If you have never used any flavor of Unix and have only used Windows or something else before, please be prepared for a lengthy period of learning.

If you already know your way around a Unix filesystem, and already know what the `/etc` folder is, how to use `vi` or `vim` or `emacs` to edit a file, how to use a shell like `tcsh` or `ksh` or `bash`, how to configure that shell, or change what shell you're using, how `su` and `doas` or `sudo` work, and what a `root` account is, the rest of this page may be enough to orient you to your surroundings.


## Software/Programs and Configuration Files Location 

The DragonFly default installation contains the base software/programs from the DragonFly project itself and additional software from other sources. 

The base system binary software programs are located in the folders 

    /bin/
    /sbin/
    /usr/bin/
    /usr/sbin/

The configuration files for the base system can be found in `/etc`. Third-party programs use `/usr/local/etc`.

There are several different ways to install software and which version you use depends on which DragonFly BSD version you have.  You can compile things from source code, or you can use binary packages.

## Disk layout of a New Dragonfly BSD System using the HAMMER2 filesystem

HAMMER2 is now the default filesystem selected by the installer.  It is not quite as feature-full as HAMMER in that there are no automatic snapshots and no undo feature, but HAMMER2 is more robust than HAMMER1 and also sports writable snapshots whereas HAMMER1 only has read-only snapshots.  HAMMER2 is also a bit easier to manage.

If you chose to install on the HAMMER2 file system during installation you will be left with a system with the following disk configuration:

    # df -h
    Filesystem                Size   Used  Avail Capacity  Mounted on
    /dev/serno/9VMBWDM1.s1d   288G    12G   276G     4%    /
    devfs                     1.0K   1.0K     0B   100%    /dev
    /dev/serno/9VMBWDM1.s1a     1G   500M   500M    50%    /boot
    /dev/serno/9VMBWDM1.s1e   100G     1M   100G     0%    /build
    /build/usr.obj               *      *      *      *    /usr/obj
    /build/usr.distfiles         *      *      *      *    /usr/distfiles
    /build/var.cache             *      *      *      *    /var/cache
    /build/var.crash             *      *      *      *    /var/crash
    tmpfs                       8G     0B     8G     0%    /tmp
    tmpfs                       8G     0B     8G     0%    /var/tmp
    procfs                    4.0K   4.0K     0B   100%    /proc


## Disk layout of a New Dragonfly BSD System using the older HAMMER1 filesystem

If you chose to install on the HAMMER file system during installation you will be left with a system with the following disk configuration:

    # df -h
    Filesystem                Size   Used  Avail Capacity  Mounted on
    ROOT                      288G    12G   276G     4%    /
    devfs                     1.0K   1.0K     0B   100%    /dev
    /dev/serno/9VMBWDM1.s1a     1G   500M   500M    50%    /boot
    /dev/serno/9VMBWDM1.s1e   100G     1M   100G     0%    /build
    /build/usr.obj               *      *      *      *    /usr/obj
    /build/usr.distfiles         *      *      *      *    /usr/distfiles
    /build/var.cache             *      *      *      *    /var/cache
    /build/var.crash             *      *      *      *    /var/crash
    tmpfs                       8G     0B     8G     0%    /tmp
    tmpfs                       8G     0B     8G     0%    /var/tmp
    procfs                    4.0K   4.0K     0B   100%    /proc

In this example

* `/dev/serno/9VMBWDM1` is the hard disk specified with serial number,
* `/dev/serno/9VMBWDM1.s1` is the first slice on the hard disk.

The disk label looks as follows:

    # disklabel /dev/serno/9VMBWDM1.s1

    # /dev/serno/9VMBWDM1.s1:
    #
    # Informational fields calculated from the above
    # All byte equivalent offsets must be aligned
    #
    # boot space:    1044992 bytes
    # data space:  312567643 blocks # 305241.84 MB (320069266944 bytes)
    #
    # NOTE: If the partition data base looks odd it may be
    #       physically aligned instead of slice-aligned
    #
    diskid: e67030af-d2af-11df-b588-01138fad54f5
    label:
    boot2 data base:      0x000000001000
    partitions data base: 0x000000100200
    partitions data stop: 0x004a85ad7000
    backup label:         0x004a85ad7000
    total size:           0x004a85ad8200    # 305242.84 MB
    alignment: 4096
    display block size: 1024        # for partition display only

    16 partitions:
    #          size     offset    fstype   fsuuid
      a:    1048576          0    4.2BSD    #    1024.000MB
      b:    8388608     786432      swap    #    8192.000MB
      d:  303392600    9175040   HAMMER2    #  296281.836MB
      e:          *          *   HAMMER2    #  blah blah ('e' partition is optional)
      a-stor_uuid: eb1c8aac-d2af-11df-b588-01138fad54f5
      b-stor_uuid: eb1c8aec-d2af-11df-b588-01138fad54f5
      d-stor_uuid: eb1c8b21-d2af-11df-b588-01138fad54f5


The slice has 3 or 4 partitions:

* `a` - for `/boot`
* `b` - for swap
* `d` - for `/`, a HAMMER or HAMMER2 filesystem labeled ROOT
* `e` - for `/build`, a HAMMER or HAMMER2 filesystem labeled (typically) DATA

When you create a HAMMER filesystem, you must give it a label.  Here, the installer labelled it as "ROOT" and mounted it as

    ROOT                      288G    12G   276G     4%    /

When you create a HAMMER2 filesystem the label is optional and a default will be supplied based on the partition letter.  Either BOOT, ROOT, SWAP, or DATA.

## HAMMER2 PFSs

In HAMMER2 the filesystem is typically mounted via its default label.  There is no distinction between this PFS and others you might create. You can create additional PFSs or you can snapshot an existing PFS and specify a new PFS name for the snapshot.  In HAMMER2, all snapshots must be independently mounted.  In addition, HAMMER2 snapshots are writable entities and you can use them just as you would the original filesystem.

HAMMER2 does not do automatic history, snapshotting, or undo.  You have to snapshot a filesystem manually with the 'hammer2' utility.

## HAMMER1 PFSs (only applicable to HAMMER1)

A PFS is a Pseudo File System inside a HAMMER file system. The HAMMER file system in which the PFSes are created is referred to as the root file system. You should not confuse the "root" file system with the label "ROOT": the label can be anything. The installer labeled it as ROOT because it is mounted at `/`.

Now inside the root HAMMER file system you find the installer created 7 PFSes from the `df -h` output above, let us see how they are mounted in `/etc/fstab`:

    # cat /etc/fstab

    # Device                Mountpoint      FStype  Options         Dump    Pass#
    /dev/serno/9VMBWDM1.s1a         /boot           ufs     rw      1       1
    /dev/serno/9VMBWDM1.s1b         none            swap    sw      0       0
    /dev/serno/9VMBWDM1.s1d         /               hammer  rw      1       1
    /pfs/var                /var            null    rw              0       0
    /pfs/tmp                /tmp            null    rw              0       0
    /pfs/usr                /usr            null    rw              0       0
    /pfs/home               /home           null    rw              0       0
    /pfs/usr.obj    /usr/obj                null    rw              0       0
    /pfs/var.crash  /var/crash              null    rw              0       0
    /pfs/var.tmp    /var/tmp                null    rw              0       0
    proc                    /proc           procfs  rw              0       0


The PFSes are mounted using a NULL mount because they are also HAMMER file systems. You can read more on NULL mounts at the [mount_null(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=mount_null&section=8) manpage.

You don't need to specify a size for the PFSes like you do for logical volumes inside a volume group for LVM. All the free space in the root HAMMER file system is available to all the PFSes; it can be seen in the `df -h` output above that the free space is the same for all PFSes and the root HAMMER file system.

If you look in `/var`

    # cd /var/
    # ls
    account   backups   caps   cron    empty   log   msgs   run   spool   yp  at        
    cache     crash     db     games   lib     mail  preserve   rwho  tmp

you will find the above directories.

If you look at the status of one of the PFSes, e.g. `/usr` you will see `/var/hammer` is the default snapshot directory.

    # hammer pfs-status /usr/
    /usr/   PFS #3 {
        sync-beg-tid=0x0000000000000001
        sync-end-tid=0x0000000117ac6270
        shared-uuid=f33e318e-d2af-11df-b588-01138fad54f5
        unique-uuid=f33e31cb-d2af-11df-b588-01138fad54f5
        label=""
        prune-min=00:00:00
        operating as a MASTER
        snapshots directory defaults to /var/hammer/<pfs>
    }

At installation time, it will be seen that there is no `hammer` directory in `/var`. The reason for this is that no snapshots have yet been taken. You can verify this by checking the snapshots available for `/usr`

    # hammer snapls /usr
    Snapshots on /usr       PFS #3
    Transaction ID          Timestamp               Note

Snapshots will appear automatically each night as the system performs housekeeping on the Hammer filesystem.  For a new volume, an immediate snapshot can be taken by running the command 'hammer cleanup'.  Among other activities, it will take a snapshot of the filesystem.

    # sudo hammer cleanup
    cleanup /                    - HAMMER UPGRADE: Creating snapshots
            Creating snapshots in /var/hammer/root
     handle PFS #0 using /var/hammer/root
               snapshots - run
                   prune - run
               rebalance - run..
                 reblock - run....
                  recopy - run....
    cleanup /var                 - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /tmp                 - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /usr                 - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /home                - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /usr/obj             - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /var/crash           - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /var/tmp             - HAMMER UPGRADE: Creating snapshots
    [...]
    cleanup /var/isos            - HAMMER UPGRADE: Creating snapshots
    [...]

No snapshots were taken for `/tmp`, `/usr/obj` and `/var/tmp`. This is because the PFSes are flagged as `nohistory`. HAMMER tracks history for all files in a PFS.  Naturally, this consumes disk space until  history is pruned, at which point the available disk space will stabilise. To prevent temporary files on the mentioned PFSes (e.g., object files, crash dumps) from consuming disk space, the PFSes are marked as `nohistory`.

After performing nightly housekeeping, a new directory called *hammer* will be found in `/var` with the following sub directories:

    # cd hammer/
    # ls -l
    total 0
    drwxr-xr-x  1 root  wheel  0 Oct 13 11:51 home
    drwxr-xr-x  1 root  wheel  0 Oct 13 11:42 root
    drwxr-xr-x  1 root  wheel  0 Oct 13 11:43 tmp
    drwxr-xr-x  1 root  wheel  0 Oct 13 11:51 usr
    drwxr-xr-x  1 root  wheel  0 Oct 13 11:54 var


Looking inside `/var/hammer/usr`, one finds:

    # cd usr/
    # ls -l
    total 0
    drwxr-xr-x  1 root  wheel   0 Oct 13 11:54 obj
    lrwxr-xr-x  1 root  wheel  25 Oct 13 11:43 snap-20101013-1143 -> /usr/@@0x0000000117ac6cb0


We have a symlink pointing to the snapshot transaction ID shown below.

    # hammer snapls /usr
    Snapshots on /usr       PFS #3
    Transaction ID          Timestamp               Note
    0x0000000117ac6cb0      2010-10-13 11:43:04 IST -
    #

You can read more about snapshots, prune, rebalance, reblock, recopy etc from [hammer(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=hammer&section=8).  Make especially sure to look under the heading "cleanup [filesystem ...]".

You can learn more about PFS mirroring [here](http://www.dragonflybsd.org/docs/how_to_implement_hammer_pseudo_file_system__40___pfs___41___slave_mirroring_from_pfs_master/)

In order to correctly map hard disk sernos to device names you can use the 'devattr' command.

    # udevd
    # devattr -d "ad*" -p serno
    Device ad4:
            serno = Z2AD9WN4
    Device ad4s1:
    Device ad4s1d:

    Device ad5:
            serno = 9VMRFDSY
    Device ad5s1:
    Device ad5s1d:

    Device ad3:
            serno = Z2AD9WLW
    Device ad3s1:
    Device ad3s1a:
    Device ad3s1b:
    Device ad3s1d:

If your disks are 'da', change as appropriate.

## OpenSSH 

 **OpenSSH**  is a set of network connectivity tools used to access remote machines securely. It can be used as a direct replacement for `rlogin`, `rsh`, `rcp`, and `telnet`. Additionally, any other TCP/IP connections can be tunneled/forwarded securely through SSH.  **OpenSSH**  encrypts all traffic to effectively eliminate eavesdropping, connection hijacking, and other network-level attacks.

 **OpenSSH**  is maintained by the OpenBSD project, and is based upon SSH v1.2.12 with all the recent bug fixes and updates. It is compatible with both SSH protocols 1 and 2.

### Advantages of Using OpenSSH 

Normally, when using telnet(1) or rlogin(1), data is sent over the network in an clear, un-encrypted form. Network sniffers anywhere in between the client and server can steal your user/password information or data transferred in your session.  **OpenSSH**  offers a variety of authentication and encryption methods to prevent this from happening.

### SSH Client 

The ssh(1) utility works similarly to rlogin(1), at this point if you try to ssh to the DragonFly you will get the following error:

    % ssh sgeorge@172.16.50.62
    The authenticity of host '172.16.50.62 (172.16.50.62)' can't be established.
    RSA key fingerprint is 46:77:28:c2:70:86:93:1a:23:32:5f:01:2c:80:de:de.
    Are you sure you want to continue connecting (yes/no)? yes
    Warning: Permanently added '172.16.50.62' (RSA) to the list of known hosts.
    Permission denied (publickey,password,keyboard-interactive).

This is because of the following configuration option in the default **/etc/ssh/sshd_config** file:

    # To disable tunneled clear text passwords, change to no here!
    PasswordAuthentication no

Change it to:

    PasswordAuthentication yes

and reload **sshd** configuration:

    # /etc/rc.d/sshd reload
    Reloading sshd config files.

Now you can login to the dragonfly system as a normal user:

    % ssh sgeorge@172.16.50.62
    sgeorge at 172.16.50.62's password:

The login will continue just as it would have if a session was created using `rlogin` or `telnet`. SSH utilizes a key fingerprint system for verifying the authenticity of the server when the client connects. The user is prompted to enter `yes` only when connecting for the first time. Future attempts to login are all verified against the saved fingerprint key. The SSH client will alert you if the saved fingerprint differs from the received fingerprint on future login attempts. The fingerprints are saved in **~/.ssh/known_hosts**, or **~/.ssh/known_hosts2** for SSH v2 fingerprints.

By default,  **OpenSSH**  servers are configured to accept both SSH v1 and SSH v2 connections. The client, however, can choose between the two. Version 2 is known to be more robust and secure than its predecessor.

The ssh(1) command can be forced to use either protocol by passing it the `-1` or `-2` argument for v1 and v2, respectively.

### Secure Copy 

The scp(1) command works similarly to rcp(1); it copies a file to or from a remote machine, except in a secure fashion.

    #  scp user@example.com:/COPYRIGHT COPYRIGHT
    user@example.com's password: *******
    COPYRIGHT            100% |*****************************|  4735
    00:00
    #

The arguments passed to scp(1) are similar to cp(1), with the file or files in the first argument, and the destination in the second. Since the file is fetched over the network, through SSH, one or more of the file arguments takes on the form `user@host:<path_to_remote_file>`. The `user@` part is optional. If omitted, it will default to the same username as you are currently logged in as, unless configured otherwise.

### Configuration 

The system-wide configuration files for both the  **OpenSSH**  daemon and client reside within the **/etc/ssh** directory.

If you look in **/etc/ssh**, you will find the SSH host key files:

    % ls /etc/ssh
    moduli                          ssh_host_ecdsa_key              ssh_host_rsa_key
    ssh_config                      ssh_host_ecdsa_key.pub          ssh_host_rsa_key.pub
    ssh_host_dsa_key                ssh_host_ed25519_key            sshd_config
    ssh_host_dsa_key.pub            ssh_host_ed25519_key.pub

**ssh_config** configures the client settings, while **sshd_config** configures the daemon.

Additionally, the **sshd_program** (**/usr/sbin/sshd** by default), and **sshd_flags** rc.conf(5) options can provide more levels of configuration.

Each user can have a personal configuration file in **~/.ssh/config**. The file can configure various client options, and can include host-specific options. With the following configuration file, a user could type **ssh shell** which would be equivalent to **ssh -X user@shell.example.com**:

    Host shell
    Hostname shell.example.com
    Username user
    Protocol 2
    ForwardX11 yes

### Login as root

If you try to login by SSH as root you will get the following error.

    % ssh root@172.16.50.62
    root at 172.16.50.62's password:
    Permission denied, please try again.

If you investigate the log of the dragonfly system **/var/log/auth.log** you will find a line similar to:

    Oct 19 07:29:36 dfly-vmsrv sshd[17269]: Failed password for root from 172.16.2.0 port 56447 ssh2

even if you typed the right password for root.

If you want to log in as root, change the following line in **/etc/ssh/sshd_config** file:

    #PermitRootLogin prohibit-password

to:

    PermitRootLogin yes

and reload **sshd** configuration:

    # /etc/rc.d/sshd reload
    Reloading sshd config files.

you can login as root:

    % ssh root@172.16.50.62
    root at 172.16.50.62's password:
    Last login: Fri Jan 12 02:01:22 2018
    DragonFly v5.0.2-RELEASE (X86_64_GENERIC) #4: Sun Dec  3 17:42:25 EST 2017

    Welcome to DragonFly!

    #

Now in the **/var/log/auth.log** you will find a line similar to

    Oct 19 07:30:32 dfly-vmsrv sshd[17894]: Accepted password for root from 172.16.2.0 port 56468 ssh2

####WARNING:

It is not advisable to allow Root Login with password especially if your System is connected to the Internet unless you use Very Strong Passwords. You could be a victim of [ssh password based brute force attacks](http://en.wikipedia.org/wiki/Password_cracking). If you are victim of one such attack you can find entries like the following in your **/var/log/auth.log** file.

    Oct 18 18:54:54 cross sshd[9783]: Invalid user maryse from 218.248.26.6
    Oct 18 18:54:54 cross sshd[9781]: input_userauth_request: invalid user maryse
    Oct 18 18:54:54 cross sshd[9783]: Failed password for invalid user maryse from 218.248.26.6 port 34847 ssh2
    Oct 18 18:54:54 cross sshd[9781]: Received disconnect from 218.248.26.6: 11: Bye Bye
    Oct 18 18:54:55 cross sshd[27641]: Invalid user may from 218.248.26.6
    Oct 18 18:54:55 cross sshd[3450]: input_userauth_request: invalid user may
    Oct 18 18:54:55 cross sshd[27641]: Failed password for invalid user may from 218.248.26.6 port 34876 ssh2
    Oct 18 18:54:55 cross sshd[3450]: Received disconnect from 218.248.26.6: 11: Bye Bye
    Oct 18 18:54:56 cross sshd[8423]: Invalid user admin from 218.248.26.6
    Oct 18 18:54:56 cross sshd[3131]: input_userauth_request: invalid user admin
    Oct 18 18:54:56 cross sshd[8423]: Failed password for invalid user admin from 218.248.26.6 port 34905 ssh2
    Oct 18 18:54:56 cross sshd[3131]: Received disconnect from 218.248.26.6: 11: Bye Bye
    Oct 18 18:54:57 cross sshd[7373]: Invalid user admin from 218.248.26.6
    Oct 18 18:54:57 cross sshd[28059]: input_userauth_request: invalid user admin
    Oct 18 18:54:57 cross sshd[7373]: Failed password for invalid user admin from 218.248.26.6 port 34930 ssh2
    Oct 18 18:54:57 cross sshd[28059]: Received disconnect from 218.248.26.6: 11: Bye Bye
    Oct 18 18:54:58 cross sshd[12081]: Invalid user admin from 218.248.26.6
    Oct 18 18:54:58 cross sshd[22416]: input_userauth_request: invalid user admin
    Oct 18 18:54:58 cross sshd[12081]: Failed password for invalid user admin from 218.248.26.6 port 34958 ssh2
    Oct 18 18:54:58 cross sshd[22416]: Received disconnect from 218.248.26.6: 11: Bye Bye

### ssh-keygen 

Instead of using passwords, ssh-keygen(1) can be used to generate RSA keys to authenticate a user:

    % ssh-keygen -t rsa1
    Initializing random number generator...
    Generating p:  .++ (distance 66)
    Generating q:  ..............................++ (distance 498)
    Computing the keys...
    Key generation complete.
    Enter file in which to save the key (/home/user/.ssh/identity):
    Enter passphrase:
    Enter the same passphrase again:
    Your identification has been saved in /home/user/.ssh/identity.
    ...

ssh-keygen(1) will create a public and private key pair for use in authentication. The private key is stored in `~/.ssh/identity`, whereas the public key is stored in `~/.ssh/identity.pub`. The public key must be placed in `~/.ssh/authorized_keys` of the remote machine in order for the setup to work.

This will allow connection to the remote machine based upon RSA authentication instead of passwords.

 **Note:** The `-t rsa1` option will create RSA keys for use by SSH protocol version 1. If you want to use RSA keys with the SSH protocol version 2, you have to use the command `ssh-keygen -t rsa`.

If a passphrase is used in ssh-keygen(1), the user will be prompted for a password each time in order to use the private key.

A SSH protocol version 2 DSA key can be created for the same purpose by using the `ssh-keygen -t dsa` command. This will create a public/private DSA key for use in SSH protocol version 2 sessions only. The public key is stored in `~/.ssh/id_dsa.pub`, while the private key is in `~/.ssh/id_dsa`.

DSA public keys are also placed in `~/.ssh/authorized_keys` on the remote machine.

ssh-agent(1) and ssh-add(1) are utilities used in managing multiple passworded private keys.

**Warning:** The various options and files can be different according to the  **OpenSSH**  version you have on your system, to avoid problems you should consult the ssh-keygen(1)] manual page.

### SSH Tunneling 

**OpenSSH**  has the ability to create a tunnel to encapsulate another protocol in an encrypted session.

The following command tells ssh(1) to create a tunnel for  **telnet** :

    % ssh -2 -N -f -L 5023:localhost:23 user@foo.example.com

The `ssh` command is used with the following options:

`-2`

 :: Forces `ssh` to use version 2 of the protocol. (Do not use if you are working with older SSH servers)

`-N`

 :: Indicates no command, or tunnel only. If omitted, `ssh` would initiate a normal session.

`-f`

 :: Forces `ssh` to run in the background.

`-L`

 :: Indicates a local tunnel in `***localport:remotehost:remoteport***` fashion.

`user@foo.example.com`

 :: The remote SSH server.

An SSH tunnel works by creating a listen socket on `localhost` on the specified port. It then forwards any connection received on the local host/port via the SSH connection to the specified remote host and port.

In the example, port `***5023***` on `localhost` is being forwarded to port `***23***` on `localhost` of the remote machine. Since `***23***` is  **telnet** , this would create a secure  **telnet**  session through an SSH tunnel.

This can be used to wrap any number of insecure TCP protocols such as SMTP, POP3, FTP, etc.

 **Example 10-1. Using SSH to Create a Secure Tunnel for SMTP** 

    % ssh -2 -N -f -L 5025:localhost:25 user@mailserver.example.com
    user@mailserver.example.com's password: *****
    % telnet localhost 5025
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    220 mailserver.example.com ESMTP

This can be used in conjunction with an ssh-keygen(1) and additional user accounts to create a more seamless/hassle-free SSH tunneling environment. Keys can be used in place of typing a password, and the tunnels can be run as a separate user.

### Practical SSH Tunneling Examples 

#### Secure Access of a POP3 Server 

At work, there is an SSH server that accepts connections from the outside. On the same office network resides a mail server running a POP3 server. The network, or network path between your home and office may or may not be completely trustable. Because of this, you need to check your e-mail in a secure manner. The solution is to create an SSH connection to your office's SSH server, and tunnel through to the mail server:

    % ssh -2 -N -f -L 2110:mail.example.com:110 user@ssh-server.example.com
    user@ssh-server.example.com's password: ******

When the tunnel is up and running, you can point your mail client to send POP3 requests to `localhost` port 2110. A connection here will be forwarded securely across the tunnel to `mail.example.com`.

#### Bypassing a Draconian Firewall 

Some network administrators impose extremely draconian firewall rules, filtering not only incoming connections, but outgoing connections. You may be only given access to contact remote machines on ports 22 and 80 for SSH and web surfing.

You may wish to access another (perhaps non-work related) service, such as an Ogg Vorbis server to stream music. If this Ogg Vorbis server is streaming on some other port than 22 or 80, you will not be able to access it.

The solution is to create an SSH connection to a machine outside of your network's firewall, and use it to tunnel to the Ogg Vorbis server.

    % ssh -2 -N -f -L 8888:music.example.com:8000 user@unfirewalled-system.example.org
    user@unfirewalled-system.example.org's password: *******

Your streaming client can now be pointed to `localhost` port 8888, which will be forwarded over to `music.example.com` port 8000, successfully evading the firewall.