DragonFly BSD

UnixBasics

UNIX Basics

*Rewritten by Chris Shumway. *

Synopsis

The following chapter will cover the basic commands and functionality of the DragonFly operating system. Much of this material is relevant for any UNIX®-like operating system. Feel free to skim over this chapter if you are familiar with the material. If you are new to DragonFly, then you will definitely want to read through this chapter carefully.

After reading this chapter, you will know:

Virtual Consoles and Terminals

DragonFly can be used in various ways. One of them is typing commands to a text terminal. A lot of the flexibility and power of a UNIX® operating system is readily available at your hands when using DragonFly this way. This section describes what terminals and consoles are, and how you can use them in !DragonFly.

The Console

If you have not configured DragonFly to automatically start a graphical environment during startup, the system will present you with a login prompt after it boots, right after the startup scripts finish running. You will see something similar to:

Additional ABI support:.
Starting cron.
Local package initialization:.
Additional TCP options:.

Wed Feb 18 17:53:48 GMT 2009

DragonFly/i386 (Amnesiac) (ttyv0)

login: 

The messages might be a bit different on your system, but you will see something similar. The last two lines are what we are interested in right now. The second last line reads:

DragonFly/i386 (Amnesiac) (ttyv0)

This line contains some bits of information about the system you have just booted. You are looking at a DragonFlyBSD console, running on an Intel or compatible processor of the x86 architecture(1). The name of this machine (every UNIX machine has a name) is Amnesiac, and you are now looking at its system console--the ttyv0 terminal. Finally, the last line is always:

login:

This is the part where you are supposed to type in your username to log into DragonFly. The next section describes how you can do this.

Logging into DragonFly

DragonFly is a multiuser, multiprocessing system. This is the formal description that is usually given to a system that can be used by many different people, who simultaneously run a lot of programs on a single machine. Every multiuser system needs some way to distinguish one userfrom the rest. In DragonFly (and every other kind of UNIX and UNIX-like operating system), this is accomplished by requiring that every user must log into the system before being able to run programs. Every user has a unique name (the username and a personal, secret key (the password). DragonFly will ask for these two before allowing a user to run any programs.

Right after DragonFly boots and finishes running its startup scripts(2), it will present you with a prompt and ask for a valid username:

login:

For the sake of this example, let us assume that your username is john. Type john at this prompt and press Enter . You should then be presented with a prompt to enter a password:

login: john
Password:

Type in john's password now, and press Enter . The password is not echoed! You need not worry about this right now. Suffice it to say that it is done for security reasons. If you have typed your password correctly, you should by now be logged into DragonFly and ready to try out all the available commands. You should see the MOTD or message of the day followed by a command prompt (a #, $, or % character). This indicates you have successfully logged into DragonFly.

Multiple Consoles

Running UNIX commands in one console is fine, but DragonFly can run many programs at once. Having one console where commands can be typed would be a bit of a waste when an operating system like DragonFly can run dozens of programs at the same time. This is where virtual consoles can be very helpful. DragonFly can be configured to present you with many different virtual consoles. You can switch from one of them to any other virtual console by pressing a couple of keys on your keyboard. Each console has its own different output channel, and DragonFly takes care of properly redirecting keyboard input and monitor output as you switch from one virtual console to the next.

Special key combinations have been reserved by DragonFly for switching consoles(3). You can use Alt - F1 , Alt - F2 , through Alt - F8 to switch to a different virtual console in DragonFly. As you are switching from one console to the next, DragonFly takes care of saving and restoring the screen output. The result is an illusion of having multiple virtual screens and keyboards that you can use to type commands for DragonFly to run. The programs that you launch on one virtual console do not stop running when that console is not visible. They continue running when you have switched to a different virtual console.

The /etc/ttys File

The default configuration of DragonFly will start up with eight virtual consoles. This is not a hardwired setting though, and you can easily customize your installation to boot with more or fewer virtual consoles. The number and settings of the virtual consoles are configured in the /etc/ttys file.

You can use the /etc/ttys file to configure the virtual consoles of DragonFly. Each uncommented line in this file (lines that do not start with a # character) contains settings for a single terminal or virtual console. The default version of this file that ships with DragonFly configures nine virtual consoles, and enables eight of them. They are the lines that start with ttyv:

# name  getty                           type    status          comments
#
ttyv0   "/usr/libexec/getty Pc"         cons25  on  secure
# Virtual terminals
ttyv1   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv2   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv3   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv4   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv5   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv6   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv7   "/usr/libexec/getty Pc"         cons25  on  secure
ttyv8   "/usr/pkg/xorg/bin/xdm -nodaemon"  xterm   off secure

For a detailed description of every column in this file and all the options you can use to set things up for the virtual consoles, consult the ttys(5) manual page.

Single User Mode Console

A detailed description of what single user mode is can be found in [boot-init.html#BOOT-SINGLEUSER Section 7.5.2]. It is worth noting that there is only one console when you are running DragonFly in single user mode. There are no virtual consoles available. The settings of the single user mode console can also be found in the /etc/ttys file. Look for the line that starts with console:

# name  getty                           type    status          comments
#
# If console is marked "insecure", then init will ask for the root password
# when going to single-user mode.
console none                            unknown off secure

Note: As the comments above the console line indicate, you can edit this line and change secure to insecure. If you do that, when DragonFly boots into single user mode, it will still ask for the root password. Be careful when changing this to insecure. If you ever forget the root password, booting into single user mode is a bit involved. It is still possible, but it might be a bit hard for someone who is not very comfortable with the DragonFly booting process and the programs involved.

Notes

(1) This is what i386 means. Note that even if you are not running DragonFly on an Intel 386 CPU, this is going to be i386. It is not the type of your processor, but the processor architecture that is shown here.
(2) Startup scripts are programs that are run automatically by DragonFly when booting. Their main function is to set things up for everything else to run, and start any services that you have configured to run in the background doing useful things.
(3) A fairly technical and accurate description of all the details of the DragonFly console and keyboard drivers can be found in the manual pages of syscons(4), atkbd(4), vidcontrol(1) and kbdcontrol(1). We will not expand on the details here, but the interested reader can always consult the manual pages for a more detailed and thorough explanation of how things work.

Permissions

DragonFly, being a direct descendant of BSD UNIX®, is based on several key UNIX concepts. The first and most pronounced is that DragonFly is a multi-user operating system. The system can handle several users all working simultaneously on completely unrelated tasks. The system is responsible for properly sharing and managing requests for hardware devices, peripherals, memory, and CPU time fairly to each user.

Because the system is capable of supporting multiple users, everything the system manages has a set of permissions governing who can read, write, and execute the resource. These permissions are stored as three octets broken into three pieces, one for the owner of the file, one for the group that the file belongs to, and one for everyone else. This numerical representation works like this:

Value Permission Directory Listing
0 No read, no write, no execute ---
1 No read, no write, execute --x
2 No read, write, no execute -w-
3 No read, write, execute -wx
4 Read, no write, no execute r--
5 Read, no write, execute r-x
6 Read, write, no execute rw-
7 Read, write, execute rwx

You can use the -l command line argument to ls(1) to view a long directory listing that includes a column with information about a file's permissions for the owner, group, and everyone else. For example, a ls -l in an arbitrary directory may show:

% ls -l
total 530
-rw-r--r--  1 root  wheel     512 Sep  5 12:31 myfile
-rw-r--r--  1 root  wheel     512 Sep  5 12:31 otherfile
-rw-r--r--  1 root  wheel    7680 Sep  5 12:31 email.txt
...

Here is how the first column of ls -l is broken up:

-rw-r--r--

The first (leftmost) character tells if this file is a regular file, a directory, a special character device, a socket, or any other special pseudo-file device. In this case, the - indicates a regular file. The next three characters, rw- in this example, give the permissions for the owner of the file. The next three characters, r--, give the permissions for the group that the file belongs to. The final three characters, r--, give the permissions for the rest of the world. A dash means that the permission is turned off. In the case of this file, the permissions are set so the owner can read and write to the file, the group can read the file, and the rest of the world can only read the file. According to the table above, the permissions for this file would be 644, where each digit represents the three parts of the file's permission.

This is all well and good, but how does the system control permissions on devices? DragonFly actually treats most hardware devices as a file that programs can open, read, and write data to just like any other file. These special device files are stored on the /dev directory.

Directories are also treated as files. They have read, write, and execute permissions. The executable bit for a directory has a slightly different meaning than that of files. When a directory is marked executable, it means it can be traversed into, that is, it is possible to cd (change directory) into it. This also means that within the directory it is possible to access files whose names are known (subject, of course, to the permissions on the files themselves).

In particular, in order to perform a directory listing, read permission must be set on the directory, whilst to delete a file that one knows the name of, it is necessary to have write and execute permissions to the directory containing the file. There are more permission bits, but they are primarily used in special circumstances such as setuid binaries and sticky directories. If you want more information on file permissions and how to set them, be sure to look at the chmod(1) manual page.

Symbolic Permissions

Contributed by Tom Rhodes.

Symbolic permissions, sometimes referred to as symbolic expressions, use characters in place of octal values to assign permissions to files or directories. Symbolic expressions use the syntax of (who) (action) (permissions), where the following values are available:

Option Letter Represents
(who) u User
(who) g Group owner
(who) o Other
(who) a All (world)
(action)
    +
Adding permissions
(action)
    -
Removing permissions
(action) = Explicitly set permissions
(permissions) r Read
(permissions) w Write
(permissions) x Execute
(permissions) t Sticky bit
(permissions) s Set UID or GID

These values are used with the chmod(1) command just like before, but with letters. For an example, you could use the following command to block other users from accessing FILE:

% chmod go=FILE

A comma separated list can be provided when more than one set of changes to a file must be made. For example the following command will remove the groups and world write permission on FILE, then it adds the execute permissions for everyone:

% chmod go-w,a+x FILE

DragonFly File Flags

Contributed by Tom Rhodes.

In addition to file permissions discussed previously, DragonFly supports the use of file flags. These flags add an additional level of security and control over files (but not directories), helping to ensure that in some cases not even root can remove or alter files. File flags are altered by using the chflags(1) utility, using a simple interface. For example, to enable the system undeletable flag on the file file1, issue the following command:

# chflags sunlink file1

To disable the system undeletable flag, simply issue the previous command with no in front of the sunlink. Observe:

# chflags nosunlink file1

To view the flags of this file, use the ls(1) command with the -lo flags:

# ls -lo file1

The output should look like the following:

-rw-r--r--  1 trhodes  trhodes  sunlnk 0 Mar  1 05:54 file1

Several flags may only added or removed to files by the root user. In other cases, the file owner may set these flags. It is recommended an administrator read over the chflags(1) and chflags(2) manual pages for more information.

Directory Structure

The DragonFly directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important concept to grasp is that of the root directory, /. This directory is the first one mounted at boot time and it contains the base system necessary to prepare the operating system for multi-user operation. The root directory also contains mount points for every other file system that you may want to mount.

A mount point is a directory where additional file systems can be grafted onto the root file system. This is further described in this Section. Standard mount points include /usr, /var, /tmp, /mnt, and /cdrom. These directories are usually referenced to entries in the file /etc/fstab. /etc/fstab is a table of various file systems and mount points for reference by the system. Most of the file systems in /etc/fstab are mounted automatically at boot time from the script rc(8) unless they contain the noauto option. Details can be found in this section.

A complete description of the file system hierarchy is available in hier(7). For now, a brief overview of the most common directories will suffice.

Directory Description
/ Root directory of the file system.
/bin/ User utilities fundamental to both single-user and multi-user environments.
/boot/ Programs and configuration files used during operating system bootstrap.
/boot/defaults/ Default bootstrapping configuration files; see loader.conf(5).
/dev/ Device nodes; see intro(4).
/etc/ System configuration files and scripts.
/etc/defaults/ Default system configuration files; see rc(8).
/etc/mail/ Configuration files for mail transport agents such as sendmail(8).
/etc/namedb/ named configuration files; see named(8).
/etc/periodic/ Scripts that are run daily, weekly, and monthly, via cron(8); see periodic(8).
/etc/ppp/ ppp configuration files; see ppp(8).
/mnt/ Empty directory commonly used by system administrators as a temporary mount point.
/proc/ Process file system; see procfs(5), mount_procfs(8).
/root/ Home directory for the root account.
/sbin/ System programs and administration utilities fundamental to both single-user and multi-user environments.
/tmp/ Temporary files. The contents of /tmp are usually NOT preserved across a system reboot. A memory-based file system is often mounted at /tmp. This can be automated with an entry in /etc/fstab; see mfs(8).
/usr/ The majority of user utilities and applications.
/usr/bin/ Common utilities, programming tools, and applications.
/usr/include/ Standard C include files.
/usr/lib/ Archive libraries.
/usr/libdata/ Miscellaneous utility data files.
/usr/libexec/ System daemons & system utilities (executed by other programs).
/usr/local/ Local executables, libraries, etc. Within /usr/local, the general layout sketched out by hier(7) for /usr should be used. An exceptions is the man directory, which is directly under /usr/local rather than under /usr/local/share.
/usr/obj/ Architecture-specific target tree produced by building the /usr/src tree.
/usr/pkg Used as the default destination for the files installed via the pkgsrc® tree or pkgsrc packages (optional). The configuration directory is tunable, but the default location is /usr/pkg/etc.
/usr/pkg/xorg/ Xorg distribution executables, libraries, etc (optional).
/usr/pkgsrc The pkgsrc tree for installing packages (optional).
/usr/sbin/ System daemons & system utilities (executed by users).
/usr/share/ Architecture-independent files.
/usr/src/ BSD and/or local source files.
/var/ Multi-purpose log, temporary, transient, and spool files. A memory-based file system is sometimes mounted at /var. This can be automated with an entry in /etc/fstab; see mfs(8).
/var/log/ Miscellaneous system log files.
/var/mail/ User mailbox files.
/var/spool/ Miscellaneous printer and mail system spooling directories.
/var/tmp/ Temporary files. The files are usually preserved across a system reboot, unless /var is a memory-based file system.
/var/yp NIS maps.

Disk Organization

The smallest unit of organization that DragonFly uses to find files is the filename. Filenames are case-sensitive, which means that readme.txt and README.TXT are two separate files. DragonFly does not use the extension (.txt) of a file to determine whether the file is a program, or a document, or some other form of data.

Files are stored in directories. A directory may contain no files, or it may contain many hundreds of files. A directory can also contain other directories, allowing you to build up a hierarchy of directories within one another. This makes it much easier to organize your data.

Files and directories are referenced by giving the file or directory name, followed by a forward slash, /, followed by any other directory names that are necessary. If you have directory foo, which contains directory bar, which contains the file readme.txt, then the full name, or path to the file is foo/bar/readme.txt.

Directories and files are stored in a file system. Each file system contains exactly one directory at the very top level, called the root directory for that file system. This root directory can then contain other directories.

So far this is probably similar to any other operating system you may have used. There are a few differences; for example, MS-DOS® and Windows® use \.

DragonFly does not use drive letters, or other drive names in the path. You would not write c:/foo/bar/readme.txt on DragonFly.

Instead, one file system is designated the root file system. The root file system's root directory is referred to as /. Every other file system is then mounted under the root file system. No matter how many disks you have on your DragonFly system, every directory appears to be part of the same disk.

Suppose you have three file systems, called A, B, and C. Each file system has one root directory, which contains two other directories, called A1, A2 (and likewise B1, B2 and C1, C2).

Call A the root file system. If you used the ls command to view the contents of this directory you would see two subdirectories, A1 and A2. The directory tree looks like this:

A file system must be mounted on to a directory in another file system. So now suppose that you mount file system B on to the directory A1. The root directory of B replaces A1, and the directories in B appear accordingly:

Any files that are in the B1 or B2 directories can be reached with the path /A1/B1 or /A1/B2 as necessary. Any files that were in /A1 have been temporarily hidden. They will reappear if B is unmounted from A.

If B had been mounted on A2 then the diagram would look like this:

and the paths would be /A2/B1 and /A2/B2 respectively.

File systems can be mounted on top of one another. Continuing the last example, the C file system could be mounted on top of the B1 directory in the B file system, leading to this arrangement:

Or C could be mounted directly on to the A file system, under the A1 directory:

If you are familiar with MS-DOS, this is similar, although not identical, to the join command.

The fstab File

During the boot process, file systems listed in /etc/fstab are automatically mounted (unless they are listed with the noauto option).

The /etc/fstab file contains a list of lines of the following format:

device       mount-point   fstype     options      dumpfreq     passno

These parameters have the following meaning:

Consult the fstab(5) manual page for more information on the format of the /etc/fstab file and the options it contains.

The mount Command

The mount(8) command is what is ultimately used to mount file systems.

In its most basic form, you use:

# mount device mountpoint

Or, if mountpoint is specified in /etc/fstab, just:

# mount mountpoint

There are plenty of options, as mentioned in the mount(8) manual page, but the most common are:

Mount Options

The -o option takes a comma-separated list of the options, including the following:

The umount Command

The umount(8) command takes, as a parameter, one of a mountpoint, a device name, or the -a or -A option.

All forms take -f to force unmounting, and -v for verbosity. Be warned that -f is not generally a good idea. Forcibly unmounting file systems might crash the computer or damage data on the file system.

-a and -A are used to unmount all mounted file systems, possibly modified by the file system types listed after -t. -A, however, does not attempt to unmount the root file system.

Choosing File System Layout

This is not normally something you need to concern yourself with. Typically you create file systems when installing DragonFly and decide where to mount them, and then never change them unless you add a new disk.

It is entirely possible to have one large root file system, and not need to create any others. There are some drawbacks to this approach, and one advantage.

Benefits of Multiple File Systems

Disk Slices, Partitions and local UNIX file systems

* Heavily edited by Nick Matavka*

DragonFly BSD divides disks into partitions and slices; it refers to locations on a disk by means of their unique codes. For instance, the disk code ad1s3d has a clear meaning: IDE hard disk one, slice three, root file system. Meanings for other such codes will become apparent by the end of this section; first of all come the meanings for the physical drive codes. The most common are:

Code Meaning
ad ATAPI (IDE) disk
da SCSI direct access disk
acd ATAPI (IDE) CDROM
cd SCSI CDROM
vn Virtual disk
fd Floppy disk

Slices

In BSD UNIX, including DragonFly, what are elsewhere known as partitions are instead known as slices; on a multi-boot system, every operating system occupies at least one slice and is aware of the others. Linux, and most UNIX operating systems, generally occupy at least two slices, one for the file system and one for swap space; on the other hand, BSD (with the exception of MacOS/DarwinBSD) may occupy only one slice, using an alternative method (called partitioning in BSD) to segregate file system and swap space. Programs such as parted and gparted, contrary to their names, are in fact disk slicers.

In DragonFly, disk slices are designated with the letter s for slice and a positive integer, beginning either from zero or one, depending on the slicing scheme. The first slice of a physical disk is thus named s0; the second, s1; and so on. There can only be four physical slices on a disk, but one of these, designated the extended slice, may itself be sliced into logical slices. If an extended slice exists, the logical slices it contains are numbered beginning with s5.

For instance, the disk ad6 may be divided into physical slices ad6s1, ad6s2 (the extended slice, containing logical slices ad6s5 and ad6s6), and ad6s3. Note that if there are less than four physical slices, the relevant numbers are skipped, even if there are logical slices.

DragonFly support two schemes for slices, MBR and GPT. Either of them can manage all of the slices on a disk:

NOTE: DragonFly doesn't support booting from a GPT slice in DragonFly 2.0. DragonFly 2.1 does have some support for booting from a GPT slice, this is described in gpt(8).

Partitions

Uniquely in BSD, disk slices contain disklabel partitions, not to be confused with the word partition in its usual meaning (that kind of partition is called a slice in BSD). In most variants of UNIX, at least two slices are used to contain the system: one for the primary file system, and one for swap space. With one exception, BSD can dispense with slices entirely and use a utility known as disklabel (or bsdlabel) to partition the disk instead.

All BSD UNIX operating systems support eight partitions per slice, labelled a through h; most BSD systems, DragonFly included, support an additional eight, labelled i through p, for a total of sixteen per slice. Partition layout is defined in a label on the slice where they reside. Since each partition may have its own file system, in BSD, one slice may be formatted in several different file systems (a situation that does not hold true in Linux or Windows).

Partition layout is defined in a label on the slice where the partition reside. DragonFly support two types of disk labels, disklabel32 and disklabel64 (the default):

By convention, four partition labels are reserved by the system and have special meanings. The convention does not strictly have to hold true, but it is highly recommended to follow this gentleman's agreement:

Partition Convention
a Normally contains the root file system
b Normally contains swap space
c Normally the same size as the enclosing slice. This allows utilities that need to work on the entire slice (for example, a bad block scanner) to work on the c partition. You would not normally create a file system on this partition. This is not necessarily true; it is possible to use the 'c' partition as a normal partition.
d Normally the same size as the entire physical disk. This is now rare, but to this day, some tools may operate oddly if told to work on partition d.

Local UNIX file systems

Each partition can contain only one file system. Therefore, file systems often are described by either their typical mount point in the file system hierarchy, or the letter of the disklabel partition they are contained in. DragonFly BSD supports two local UNIX file systems, UFS and HAMMER:

Historically, the desirability of HAMMERfs increased with storage capacity. For booting DragonFly from a small, local file system, UFS was previously recommended, with the option of a BOOT+HAMMER set up (512 MB UFS boot partition, the rest HAMMERfs). For moderate storage requirements, UFS continued to be an option, but the extra features boasted by HAMMERfs (such as history retention) made it more desirable in this regard.
Then, as now, HAMMERfs was the unrivalled king of the large partition, usually with a disklabel64(8) label on a GPT slice.

As of DragonFly version 3.6, this question is mostly, or entirely, of academic interest. HAMMERfs is now recommended for all volumes greater than eighty gigabytes---that is to say, all volumes manufactured within the last five years, and a goodly portion of older ones as well.

The HAMMER File System

HAMMER(5) is a rather new file system, under active development. HAMMERfs reached beta in release 2.0. As of release 2.2.1, HAMMERfs is considered to be appropriate for use in the production environment; DragonFly is currently in release 3.6.

If you are deploying DragonFly on a low-capacity, low-memory system, you should evaluate if HAMMERfs is suitable for your needs; for a personal computer or server of even medium vintage, no thought need go into this, as it will be found that HAMMERfs is the file system of choice. HAMMER(5) has several advanced features not found in UFS:

All these features are subordinate to the single, basic, overarching purpose of the HAMMER file system: full history retention. With HAMMERfs, all file system changes are saved every ~30 seconds. Changes are written at least when sync() is called (see syncer(4)). Every time data are written to disk, a transaction is completed, this is assigned an identifier, and the file updated can after this be accessed with the contents from this moment.

To access the file as it was then, all the user must do is add the transaction identifier to the file name, in the form file@@<tid>. The TID can be saved from the snapshot, cleanup, or synctid hammer(8) command, or looked up with the hammer history file command. This history will typically grow over time, so any disk will fill up over time.

Two things are done so the disk does not fill up too fast, or too much. First of all, at least moderately large disks are used. Second, HAMMER can be made self-managing with a policy for which history to save for how long. For example, make a snapshot every hour and prune and reblock (hammer(8)) regularly. When snapshots get older than one month, keep them for six hours; when older than three months, keep them for a day; when older than three years, keep them for a month.

Historically, you needed to set up cron(8) jobs for this yourself, but HAMMER now includes a utility to make this easy.

Adding a Disk

Adding a disk is done by installing it physically and by connecting it to a disk controller supported by DragonFly BSD. If you are in doubt as to whether a particular disk controller is supported, the manual pages for disk controllers can be consulted (man -k disk or man -k scsi can be of help). Another, easier way of ascertaining support for a controller is to boot with the controller installed, and note if the boot messages contain the controller.

Assuming that disk ad6 is installed, we could set it up the old-fashioned way, using fdisk(8) and disklabel(8)](http://leaf.dragonflybsd.org/cgi/web-man?command=disklabel&section8) or the modern way, with gpt(8) and disklabel64(8), or any combination thereof.

In this example, we chose gpt(8) and disklabel64(8).

# gpt -v create ad6
[...]
# gpt add -s1 ad6
ad6s0
# gpt add ad6
ad6s1
# gpt show ad6
[...]

In the above example, we first create the GPT and then add two slices. The first slice added is ad6s0, which is made a dummy slice of size 1 sector. The reason for this is backwards compatibility: veteran users may remember that s0 has special meaning in MBR slice schemes, but this is not true in GPT slices. The second slice, ad6s1, will cover the rest of the disk:

# disklabel64 -rw ad6s1 auto
# disklabel64 -e ad6s1          # edit label to add partitions as needed

Processes

DragonFly is a multi-tasking operating system. This means that it seems as though more than one program is running at once. Each program running at any one time is called a process. Every command you run will start at least one new process, and there are a number of system processes that run all the time, keeping the system functional.

Each process is uniquely identified by a number called a process ID, or PID, and, like files, each process also has one owner and group. The owner and group information is used to determine what files and devices the process can open, using the file permissions discussed earlier. Most processes also have a parent process. The parent process is the process that started them. For example, if you are typing commands to the shell then the shell is a process, and any commands you run are also processes. Each process you run in this way will have your shell as its parent process. The exception to this is a special process called init(8). init is always the first process, so its PID is always 1. init is started automatically by the kernel when DragonFly starts.

Two commands are particularly useful to see the processes on the system, ps(1) and top(1). The ps command is used to show a static list of the currently running processes, and can show their PID, how much memory they are using, the command line they were started with, and so on. The top command displays all the running processes, and updates the display every few seconds, so that you can interactively see what your computer is doing.

By default, ps only shows you the commands that are running and are owned by you. For example:

% ps

  PID  TT  STAT      TIME COMMAND
  298  p0  Ss     0:01.10 tcsh
 7078  p0  S      2:40.88 xemacs mdoc.xsl (xemacs-21.1.14)
37393  p0  I      0:03.11 xemacs freebsd.dsl (xemacs-21.1.14)
48630  p0  S      2:50.89 /usr/local/lib/netscape-linux/navigator-linux-4.77.bi
48730  p0  IW     0:00.00 (dns helper) (navigator-linux-)
72210  p0  R+     0:00.00 ps
  390  p1  Is     0:01.14 tcsh
 7059  p2  Is+    1:36.18 /usr/local/bin/mutt -y
 6688  p3  IWs    0:00.00 tcsh
10735  p4  IWs    0:00.00 tcsh
20256  p5  IWs    0:00.00 tcsh
  262  v0  IWs    0:00.00 -tcsh (tcsh)
  270  v0  IW+    0:00.00 /bin/sh /usr/X11R6/bin/startx -- -bpp 16
  280  v0  IW+    0:00.00 xinit /home/nik/.xinitrc -- -bpp 16
  284  v0  IW     0:00.00 /bin/sh /home/nik/.xinitrc
  285  v0  S      0:38.45 /usr/X11R6/bin/sawfish

As you can see in this example, the output from ps(1) is organized into a number of columns. PID is the process ID discussed earlier. PIDs are assigned starting from 1, go up to 99999, and wrap around back to the beginning when you run out. The TT column shows the tty the program is running on, and can safely be ignored for the moment. STAT shows the program's state, and again, can be safely ignored. TIME is the amount of time the program has been running on the CPU--this is usually not the elapsed time since you started the program, as most programs spend a lot of time waiting for things to happen before they need to spend time on the CPU. Finally, COMMAND is the command line that was used to run the program.

ps(1) supports a number of different options to change the information that is displayed. One of the most useful sets is auxww. a displays information about all the running processes, not just your own. u displays the username of the process' owner, as well as memory usage. x displays information about daemon processes, and ww causes ps(1) to display the full command line, rather than truncating it once it gets too long to fit on the screen.

The output from top(1) is similar. A sample session looks like this:

% top
last pid: 72257;  load averages:  0.13,  0.09,  0.03    up 0+13:38:33  22:39:10
47 processes:  1 running, 46 sleeping
CPU states: 12.6% user,  0.0% nice,  7.8% system,  0.0% interrupt, 79.7% idle
Mem: 36M Active, 5256K Inact, 13M Wired, 6312K Cache, 15M Buf, 408K Free
Swap: 256M Total, 38M Used, 217M Free, 15% Inuse


  PID USERNAME PRI NICE  SIZE    RES STATE    TIME   WCPU    CPU COMMAND
72257 nik       28   0  1960K  1044K RUN      0:00 14.86%  1.42% top
 7078 nik        2   0 15280K 10960K select   2:54  0.88%  0.88% xemacs-21.1.14
  281 nik        2   0 18636K  7112K select   5:36  0.73%  0.73% XF86_SVGA
  296 nik        2   0  3240K  1644K select   0:12  0.05%  0.05% xterm
48630 nik        2   0 29816K  9148K select   3:18  0.00%  0.00% navigator-linu
  175 root       2   0   924K   252K select   1:41  0.00%  0.00% syslogd
 7059 nik        2   0  7260K  4644K poll     1:38  0.00%  0.00% mutt
...

The output is split into two sections. The header (the first five lines) shows the PID of the last process to run, the system load averages (which are a measure of how busy the system is), the system uptime (time since the last reboot) and the current time. The other figures in the header relate to how many processes are running (47 in this case), how much memory and swap space has been taken up, and how much time the system is spending in different CPU states.

Below that are a series of columns containing similar information to the output from ps(1). As before you can see the PID, the username, the amount of CPU time taken, and the command that was run. top(1) also defaults to showing you the amount of memory space taken by the process. This is split into two columns, one for total size, and one for resident size--total size is how much memory the application has needed, and the resident size is how much it is actually using at the moment. In this example you can see that Netscape® has required almost 30 MB of RAM, but is currently only using 9 MB.

top(1) automatically updates this display every two seconds; this can be changed with the s option.

Daemons, Signals, and Killing Processes

When you run an editor it is easy to control the editor, tell it to load files, and so on. You can do this because the editor provides facilities to do so, and because the editor is attached to a terminal. Some programs are not designed to be run with continuous user input, and so they disconnect from the terminal at the first opportunity. For example, a web server spends all day responding to web requests, it normally does not need any input from you. Programs that transport email from site to site are another example of this class of application.

We call these programs daemons. Daemons were characters in Greek mythology; neither good or evil, they were little attendant spirits that, by and large, did useful things for mankind. Much like the web servers and mail servers of today do useful things. This is why the mascot for a number of BSD-based operating systems has, for a long time, been a cheerful looking daemon with sneakers and a pitchfork.

There is a convention to name programs that normally run as daemons with a trailing d. BIND is the Berkeley Internet Name Daemon (and the actual program that executes is called named), the Apache web server program is called httpd, the line printer spooling daemon is lpd and so on. This is a convention, not a hard and fast rule; for example, the main mail daemon for the Sendmail application is called sendmail, and not maild, as you might imagine.

Sometimes you will need to communicate with a daemon process. These communications are called signals, and you can communicate with a daemon (or with any other running process) by sending it a signal. There are a number of different signals that you can send--some of them have a specific meaning, others are interpreted by the application, and the application's documentation will tell you how that application interprets signals. You can only send a signal to a process that you own. If you send a signal to someone else's process with kill(1) or kill(2) permission will be denied. The exception to this is the root user, who can send signals to everyone's processes.

DragonFly will also send applications signals in some cases. If an application is badly written, and tries to access memory that it is not supposed to, DragonFly sends the process the Segmentation Violation signal (SIGSEGV). If an application has used the alarm(3) system call to be alerted after a period of time has elapsed then it will be sent the Alarm signal (SIGALRM), and so on.

Two signals can be used to stop a process, SIGTERM and SIGKILL. SIGTERM is the polite way to kill a process; the process can catch the signal, realize that you want it to shut down, close any log files it may have open, and generally finish whatever it is doing at the time before shutting down. In some cases a process may even ignore SIGTERM if it is in the middle of some task that can not be interrupted.

SIGKILL can not be ignored by a process. This is the I do not care what you are doing, stop right now signal. If you send SIGKILL to a process then DragonFly will stop that process there and then(1).

The other signals you might want to use are SIGHUP, SIGUSR1, and SIGUSR2. These are general purpose signals, and different applications will do different things when they are sent.

Suppose that you have changed your web server's configuration file--you would like to tell the web server to re-read its configuration. You could stop and restart httpd, but this would result in a brief outage period on your web server, which may be undesirable. Most daemons are written to respond to the SIGHUP signal by re-reading their configuration file. So instead of killing and restarting httpd you would send it the SIGHUP signal. Because there is no standard way to respond to these signals, different daemons will have different behavior, so be sure and read the documentation for the daemon in question.

Signals are sent using the kill(1) command, as this example shows.

Sending a Signal to a Process

This example shows how to send a signal to inetd(8). The inetd configuration file is /etc/inetd.conf, and inetd will re-read this configuration file when it is sent SIGHUP.

  1. Find the process ID of the process you want to send the signal to. Do this using ps(1) and grep(1). The grep(1) command is used to search through output, looking for the string you specify. This command is run as a normal user, and inetd(8) is run as root, so the ax options must be given to ps(1).

    % ps -ax | grep inetd
    
    
    198  ??  IWs    0:00.00 inetd -wW
    

    So the inetd(8) PID is 198. In some cases the grep inetd command might also occur in this output. This is because of the way ps(1) has to find the list of running processes.

  2. Use kill(1) to send the signal. Because inetd(8) is being run by root you must use su(1) to become root first.

    % su
    
    
    Password:
    
    
    # /bin/kill -s HUP 198
    

    In common with most UNIX® commands, kill(1) will not print any output if it is successful. If you send a signal to a process that you do not own then you will see kill: PID: Operation not permitted. If you mistype the PID you will either send the signal to the wrong process, which could be bad, or, if you are lucky, you will have sent the signal to a PID that is not currently in use, and you will see kill: PID: No such process.

Why Use /bin/kill? Many shells provide the kill command as a built in command; that is, the shell will send the signal directly, rather than running /bin/kill. This can be very useful, but different shells have a different syntax for specifying the name of the signal to send. Rather than try to learn all of them, it can be simpler just to use the /bin/kill ... command directly.

Sending other signals is very similar, just substitute TERM or KILL in the command line as necessary.

Important: Killing random process on the system can be a bad idea. In particular, init(8), process ID 1, is very special. Running /bin/kill -s KILL 1 is a quick way to shutdown your system. Always double check the arguments you run kill(1) with before you press Return .

Shells

In DragonFly, a lot of everyday work is done in a command line interface called a shell. A shell's main job is to take commands from the input channel and execute them. A lot of shells also have built in functions to help everyday tasks such as file management, file globbing, command line editing, command macros, and environment variables. DragonFly comes with a set of shells, such as sh, the Bourne Shell, and tcsh, the improved C-shell. Many other shells are available from pkgsrc®, such as zsh and bash.

Which shell do you use? It is really a matter of taste. If you are a C programmer you might feel more comfortable with a C-like shell such as tcsh. If you have come from Linux or are new to a UNIX® command line interface you might try bash. The point is that each shell has unique properties that may or may not work with your preferred working environment, and that you have a choice of what shell to use.

One common feature in a shell is filename completion. Given the typing of the first few letters of a command or filename, you can usually have the shell automatically complete the rest of the command or filename by hitting the Tab key on the keyboard. Here is an example. Suppose you have two files called foobar and foo.bar. You want to delete foo.bar. So what you would type on the keyboard is: rm fo[ **Tab** ].[ **Tab** ].

The shell would print out rm foo[BEEP].bar.

The [BEEP] is the console bell, which is the shell telling me it was unable to totally complete the filename because there is more than one match. Both foobar and foo.bar start with fo, but it was able to complete to foo. If you type in ., then hit Tab again, the shell would be able to fill in the rest of the filename for you.

Another feature of the shell is the use of environment variables. Environment variables are a variable key pair stored in the shell's environment space. This space can be read by any program invoked by the shell, and thus contains a lot of program configuration. Here is a list of common environment variables and what they mean:

Variable Description
USER Current logged in user's name.
PATH Colon separated list of directories to search for binaries.
DISPLAY Network name of the X11 display to connect to, if available.
SHELL The current shell.
TERM The name of the user's terminal. Used to determine the capabilities of the terminal.
TERMCAP Database entry of the terminal escape codes to perform various terminal functions.
OSTYPE Type of operating system. e.g., DragonFly.
MACHTYPE The CPU architecture that the system is running on.
EDITOR The user's preferred text editor.
PAGER The user's preferred text pager.
MANPATH Colon separated list of directories to search for manual pages.

Setting an environment variable differs somewhat from shell to shell. For example, in the C-Style shells such as tcsh and csh, you would use setenv to set environment variables. Under Bourne shells such as sh and bash, you would use export to set your current environment variables. For example, to set or modify the EDITOR environment variable, under csh or tcsh a command like this would set EDITOR to /usr/pkg/bin/emacs:

% setenv EDITOR /usr/pkg/bin/emacs

Under Bourne shells:

% export EDITOR="/usr/pkg/bin/emacs"

You can also make most shells expand the environment variable by placing a $ character in front of it on the command line. For example, echo $TERM would print out whatever $TERM is set to, because the shell expands $TERM and passes it on to echo.

Shells treat a lot of special characters, called meta-characters as special representations of data. The most common one is the * character, which represents any number of characters in a filename. These special meta-characters can be used to do filename globbing. For example, typing in echo * is almost the same as typing in ls because the shell takes all the files that match * and puts them on the command line for echo to see.

To prevent the shell from interpreting these special characters, they can be escaped from the shell by putting a backslash (\) character in front of them. echo $TERM prints whatever your terminal is set to. echo \$TERM prints $TERM as is.

Changing Your Shell

The easiest way to change your shell is to use the chsh command. Running chsh will place you into the editor that is in your EDITOR environment variable; if it is not set, you will be placed in vi. Change the Shell: line accordingly.

You can also give chsh the -s option; this will set your shell for you, without requiring you to enter an editor. For example, if you wanted to change your shell to bash, the following should do the trick:

% chsh -s /usr/pkg/bin/bash

Note: The shell that you wish to use must be present in the /etc/shells file. If you have installed a shell from the pkgsrc tree , then this should have been done for you already. If you installed the shell by hand, you must do this.

For example, if you installed bash by hand and placed it into /usr/local/bin, you would want to:

# echo "/usr/local/bin/bash" >> /etc/shells

Then rerun chsh.

Text Editors

A lot of configuration in DragonFly is done by editing text files. Because of this, it would be a good idea to become familiar with a text editor. DragonFly comes with a few as part of the base system, and many more are available in the pkgsrc® tree.

The easiest and simplest editor to learn is an editor called ee , which stands for easy editor. To start ee , one would type at the command line ee filename where filename is the name of the file to be edited. For example, to edit /etc/rc.conf, type in ee /etc/rc.conf. Once inside of ee, all of the commands for manipulating the editor's functions are listed at the top of the display. The caret ^ character represents the Ctrl key on the keyboard, so ^e expands to the key combination Ctrl + e . To leave ee , hit the Esc key, then choose leave editor. The editor will prompt you to save any changes if the file has been modified.

DragonFly also comes with more powerful text editors such as vi as part of the base system, while other editors, like emacs and vim , are part of the pkgsrc tree. These editors offer much more functionality and power at the expense of being a little more complicated to learn. However if you plan on doing a lot of text editing, learning a more powerful editor such as vim or emacs will save you much more time in the long run.

Devices and Device Nodes

A device is a term used mostly for hardware-related activities in a system, including disks, printers, graphics cards, and keyboards. When DragonFly boots, the majority of what DragonFly displays are devices being detected. You can look through the boot messages again by viewing /var/run/dmesg.boot.

For example, acd0 is the first IDE CDROM drive, while kbd0 represents the keyboard.

Most of these devices in a UNIX® operating system must be accessed through special files called device nodes, which are located in the /dev directory.

The device nodes in the /dev directory are created and destroyed automatically on DragonFly >= 2.4, by means of the device file system (devfs).

Binary Formats

To understand why DragonFly uses the elf(5) format, you must first know a little about the three currently dominant executable formats for UNIX®:

So, why are there so many different formats? Back in the dim, dark past, there was simple hardware. This simple hardware supported a simple, small system. a.out was completely adequate for the job of representing binaries on this simple system (a PDP-11). As people ported UNIX from this simple system, they retained the a.out format because it was sufficient for the early ports of UNIX to architectures like the Motorola 68k, VAXen, etc.

Then some bright hardware engineer decided that if he could force software to do some sleazy tricks, then he would be able to shave a few gates off the design and allow his CPU core to run faster. While it was made to work with this new kind of hardware (known these days as RISC), a.out was ill-suited for this hardware, so many formats were developed to get to a better performance from this hardware than the limited, simple a.out format could offer. Things like COFF, ECOFF, and a few obscure others were invented and their limitations explored before things seemed to settle on ELF.

In addition, program sizes were getting huge and disks (and physical memory) were still relatively small so the concept of a shared library was born. The VM system also became more sophisticated. While each one of these advancements was done using the a.out format, its usefulness was stretched more and more with each new feature. In addition, people wanted to dynamically load things at run time, or to junk parts of their program after the init code had run to save in core memory and swap space. Languages became more sophisticated and people wanted code called before main automatically. Lots of hacks were done to the a.out format to allow all of these things to happen, and they basically worked for a time. In time, a.out was not up to handling all these problems without an ever increasing overhead in code and complexity. While ELF solved many of these problems, it would be painful to switch from the system that basically worked. So ELF had to wait until it was more painful to remain with a.out than it was to migrate to ELF.

ELF is more expressive than a.out and allows more extensibility in the base system. The ELF tools are better maintained, and offer cross compilation support, which is important to many people. ELF may be a little slower than a.out, but trying to measure it can be difficult. There are also numerous details that are different between the two in how they map pages, handle init code, etc. None of these are very important, but they are differences.

For More Information

Manual Pages

The most comprehensive documentation on DragonFly is in the form of manual pages. Nearly every program on the system comes with a short reference manual explaining the basic operation and various arguments. These manuals can be viewed with the man command. Use of the man command is simple:

% man command

command is the name of the command you wish to learn about. For example, to learn more about ls command type:

% man ls

The online manual is divided up into numbered sections:

  1. User commands.
  2. System calls and error numbers.
  3. Functions in the C libraries.
  4. Device drivers.
  5. File formats.
  6. Games and other diversions.
  7. Miscellaneous information.
  8. System maintenance and operation commands.
  9. Kernel internals.

In some cases, the same topic may appear in more than one section of the online manual. For example, there is a chmod user command and a chmod() system call. In this case, you can tell the man command which one you want by specifying the section:

% man 1 chmod

This will display the manual page for the user command chmod. References to a particular section of the online manual are traditionally placed in parenthesis in written documentation, so chmod(1) refers to the chmod user command and chmod(2) refers to the system call.

This is fine if you know the name of the command and simply wish to know how to use it, but what if you cannot recall the command name? You can use man to search for keywords in the command descriptions by using the -k switch:

% man -k mail

With this command you will be presented with a list of commands that have the keyword mail in their descriptions. This is actually functionally equivalent to using the apropos command.

So, you are looking at all those fancy commands in /usr/bin but do not have the faintest idea what most of them actually do? Simply do:

% cd /usr/bin
% man -f *

or

% cd /usr/bin
% whatis *

which does the same thing.

GNU Info Files

DragonFly includes many applications and utilities produced by the Free Software Foundation (FSF). In addition to manual pages, these programs come with more extensive hypertext documents called info files which can be viewed with the info command or, if you installed emacs , the info mode of emacs . To use the info(1) command, simply type:

% info

For a brief introduction, type h. For a quick command reference, type ?.