This chapter covers the basic commands and functionality of the FreeBSD operating system. Much of this material is relevant for any UNIX®-like operating system. New FreeBSD users are encouraged to read through this chapter carefully.

After reading this chapter, you will know:

Unless FreeBSD has been configured to automatically start a graphical environment during startup, the system will boot into a command line login prompt, as seen in this example:

The first line contains some information about the system. The amd64 indicates that the system in this example is running a 64-bit version of FreeBSD. The hostname is pc3.example.org , and ttyv0 indicates that this is the “system console” . The second line is the login prompt.

Since FreeBSD is a multiuser system, it needs some way to distinguish between different users. This is accomplished by requiring every user to log into the system before gaining access to the programs on the system. Every user has a unique name “username” and a personal “password” .

To log into the system console, type the username that was configured during system installation, as described in [_bsdinstall_addusers], and press Enter . Then enter the password associated with the username and press Enter . The password is not echoed for security reasons.

Once the correct password is input, the message of the day (MOTD) will be displayed followed by a command prompt. Depending upon the shell that was selected when the user was created, this prompt will be a \#, $, or % character. The prompt indicates that the user is now logged into the FreeBSD system console and ready to try the available commands.

FreeBSD allows multiple users to use the computer at the same time. While only one user can sit in front of the screen and use the keyboard at any one time, any number of users can log in to the system through the network. To use the system, each user should have their own user account.

This chapter describes:

In FreeBSD, every file and directory has an associated set of permissions and several utilities are available for viewing and modifying these permissions. Understanding how permissions work is necessary to make sure that users are able to access the files that they need and are unable to improperly access the files used by the operating system or owned by other users.

This section discusses the traditional UNIX® permissions used in FreeBSD. For finer grained file system access control, refer to [_fs_acl].

In UNIX®, basic permissions are assigned using three types of access: read, write, and execute. These access types are used to determine file access to the file’s owner, group, and others (everyone else). The read, write, and execute permissions can be represented as the letters r, w, and x. They can also be represented as binary numbers as each permission is either on or off (0). When represented as a number, the order is always read as rwx, where r has an on value of 4, w has an on value of 2 and x has an on value of 1.

Table 4.1 summarizes the possible numeric and alphabetic possibilities. When reading the “Directory Listing” column, a - is used to represent a permission that is set to off.

Use the -l argument to ls(1) to view a long directory listing that includes a column of information about a file’s permissions for the owner, group, and everyone else. For example, a ls -l in an arbitrary directory may show:

The first (leftmost) character in the first column indicates whether this file is a regular file, a directory, a special character device, a socket, or any other special pseudo-file device. In this example, 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 this example, 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.

How does the system control permissions on devices? FreeBSD treats most hardware devices as a file that programs can open, read, and write data to. These special device files are stored in /dev/ .

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 is possible to change into that directory using cd(1) . This also means that it is possible to access the files within that directory, subject to the permissions on the files themselves.

In order to perform a directory listing, the read permission must be set on the directory. In order 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. For more information on file permissions and how to set them, refer to chmod(1) .

The FreeBSD directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important directory is root or, “/” . 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 other file systems that are mounted during the transition to multi-user operation.

A mount point is a directory where additional file systems can be grafted onto a parent file system (usually the root file system). This is further described in Disk Organization. Standard mount points include /usr/ , /var/ , /tmp/ , /mnt/ , and /cdrom/ . These directories are usually referenced to entries in /etc/fstab . This file is a table of various file systems and mount points and is read by the system. Most of the file systems in /etc/fstab are mounted automatically at boot time from the script rc(8) unless their entry includes noauto. Details can be found in The fstab File.

A complete description of the file system hierarchy is available in hier(7) . The following table provides a brief overview of the most common directories.

The smallest unit of organization that FreeBSD uses to find files is the filename. Filenames are case-sensitive, which means that readme.txt and README.TXT are two separate files. FreeBSD does not use the extension of a file to determine whether the file is a program, 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 a hierarchy of directories within one another in order to organize 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. For example, if the directory foo contains a directory bar which contains the file readme.txt , the full name, or path , to the file is foo/bar/readme.txt . Note that this is different from Windows™ which uses \ to separate file and directory names. FreeBSD does not use drive letters, or other drive names in the path. For example, one would not type c:\foo\bar\readme.txt on FreeBSD.

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 contain other directories. One file system is designated the root file system or /. Every other file system is mounted under the root file system. No matter how many disks are on the FreeBSD system, every directory appears to be part of the same disk.

Consider 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 ls(1) is used to view the contents of this directory, it will show 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. When mounting 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:

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.

File systems are contained in partitions. This does not have the same meaning as the common usage of the term partition (for example, MS-DOS™ partition), because of FreeBSD’s UNIX® heritage. Each partition is identified by a letter from a through to h. Each partition can contain only one file system, which means that file systems are often described by either their typical mount point in the file system hierarchy, or the letter of the partition they are contained in.

FreeBSD also uses disk space for swap space to provide virtual memory . This allows your computer to behave as though it has much more memory than it actually does. When FreeBSD runs out of memory, it moves some of the data that is not currently being used to the swap space, and moves it back in (moving something else out) when it needs it.

Some partitions have certain conventions associated with them.

Disks in FreeBSD are divided into slices, referred to in Windows™ as partitions, which are numbered from 1 to 4. These are then divided into partitions, which contain file systems, and are labeled using letters.

Slice numbers follow the device name, prefixed with an s, starting at 1. So “da0s1” is the first slice on the first SCSI drive. There can only be four physical slices on a disk, but there can be logical slices inside physical slices of the appropriate type. These extended slices are numbered starting at 5, so “ada0s5” is the first extended slice on the first SATA disk. These devices are used by file systems that expect to occupy a slice.

Slices, “dangerously dedicated” physical drives, and other drives contain partitions , which are represented as letters from a to h. This letter is appended to the device name, so “da0a” is the a partition on the first da drive, which is “dangerously dedicated” . “ada1s3e” is the fifth partition in the third slice of the second SATA disk drive.

Finally, each disk on the system is identified. A disk name starts with a code that indicates the type of disk, and then a number, indicating which disk it is. Unlike slices, disk numbering starts at 0. Common codes are listed in Disk Device Names.

When referring to a partition, include the disk name, s, the slice number, and then the partition letter. Examples are shown in Sample Disk, Slice, and Partition Names.

Conceptual Model of a Disk shows a conceptual model of a disk layout.

When installing FreeBSD, configure the disk slices, create partitions within the slice to be used for FreeBSD, create a file system or swap space in each partition, and decide where each file system will be mounted.

The file system is best visualized as a tree, rooted, as it were, at / . /dev , /usr , and the other directories in the root directory are branches, which may have their own branches, such as /usr/local , and so on.

There are various reasons to house some of these directories on separate file systems. /var contains the directories log/ , spool/ , and various types of temporary files, and as such, may get filled up. Filling up the root file system is not a good idea, so splitting /var from / is often favorable.

Another common reason to contain certain directory trees on other file systems is if they are to be housed on separate physical disks, or are separate virtual disks, such as Network File System mounts, described in [_network_nfs], or CDROM drives.

FreeBSD is a multi-tasking operating system. Each program running at any one time is called a process . Every running command starts at least one new process and there are a number of system processes that are run by FreeBSD.

Each process is uniquely identified by a number called a process ID (PID). Similar to files, each process has one owner and group, and the owner and group permissions are used to determine which files and devices the process can open. Most processes also have a parent process that started them. For example, the shell is a process, and any command started in the shell is a process which has the shell as its parent process. The exception is a special process called init(8) which is always the first process to start at boot time and which always has a PID of 1.

Some programs are not designed to be run with continuous user input and disconnect from the terminal at the first opportunity. For example, a web server responds to web requests, rather than user input. Mail servers are another example of this type of application. These types of programs are known as daemons . The term daemon comes from Greek mythology and represents an entity that is neither good nor evil, and which invisibly performs useful tasks. This is why the BSD mascot is the cheerful-looking daemon with sneakers and a pitchfork.

There is a convention to name programs that normally run as daemons with a trailing “d” . For example, BIND is the Berkeley Internet Name Domain, but the actual program that executes is named. The Apache web server program is httpd and the line printer spooling daemon is lpd. This is only a naming convention. For example, the main mail daemon for the Sendmail application is sendmail, and not maild.

A shell provides a command line interface for interacting with the operating system. A shell receives commands from the input channel and executes them. Many shells provide built in functions to help with everyday tasks such as file management, file globbing, command line editing, command macros, and environment variables. FreeBSD comes with several shells, including the Bourne shell ( sh(1) ) and the extended C shell ( tcsh(1) ). Other shells are available from the FreeBSD Ports Collection, such as zsh and bash.

The shell that is used is really a matter of taste. A C programmer might feel more comfortable with a C-like shell such as tcsh(1) . A Linux™ user might prefer bash. Each shell has unique properties that may or may not work with a user’s preferred working environment, which is why there is a choice of which shell to use.

One common shell feature is filename completion. After a user types the first few letters of a command or filename and presses Tab , the shell completes the rest of the command or filename. Consider two files called foobar and football . To delete foobar , the user might type rm foo and press Tab to complete the filename.

But the shell only shows rm foo. It was unable to complete the filename because both foobar and football start with foo. Some shells sound a beep or show all the choices if more than one name matches. The user must then type more characters to identify the desired filename. Typing a t and pressing Tab again is enough to let the shell determine which filename is desired and fill in the rest.

Another feature of the shell is the use of environment variables. Environment variables are a variable/key pair stored in the shell’s environment. This environment can be read by any program invoked by the shell, and thus contains a lot of program configuration. Common Environment Variables provides a list of common environment variables and their meanings. Note that the names of environment variables are always in uppercase.

How to set an environment variable differs between shells. In tcsh(1) and csh(1) , use setenv to set environment variables. In sh(1) and bash, use export to set the current environment variables. This example sets the default EDITOR to /usr/local/bin/emacs for the tcsh(1) shell:

The equivalent command for bash would be:

To expand an environment variable in order to see its current setting, type a $ character in front of its name on the command line. For example, echo $TERM displays the current $TERM setting.

Shells treat special characters, known as meta-characters, as special representations of data. The most common meta-character is *, which represents any number of characters in a filename. Meta-characters can be used to perform filename globbing. For example, echo * is equivalent to ls because the shell takes all the files that match \* and echo lists them on the command line.

To prevent the shell from interpreting a special character, escape it from the shell by starting it with a backslash (\). For example, echo $TERM prints the terminal setting whereas echo \$TERM literally prints the string $TERM.

Most FreeBSD configuration is done by editing text files. Because of this, it is a good idea to become familiar with a text editor. FreeBSD comes with a few as part of the base system, and many more are available in the Ports Collection.

A simple editor to learn is ee(1) , which stands for easy editor. To start this editor, type ee [replaceable]filename` where [replaceable]filename is the name of the file to be edited. Once inside the editor, all of the commands for manipulating the editor’s functions are listed at the top of the display. The caret (^`) represents Ctrl , so ^e expands to Ctrl+e . To leave ee(1) , press Esc , then choose the “leave editor” option from the main menu. The editor will prompt to save any changes if the file has been modified.

FreeBSD also comes with more powerful text editors, such as vi(1) , as part of the base system. Other editors, like editors/emacs and editors/vim , are part of the FreeBSD Ports Collection. These editors offer more functionality at the expense of being more complicated to learn. Learning a more powerful editor such as vim or Emacs can save more time in the long run.

Many applications which modify files or require typed input will automatically open a text editor. To change the default editor, set the EDITOR environment variable as described in Shells.

A device is a term used mostly for hardware-related activities in a system, including disks, printers, graphics cards, and keyboards. When FreeBSD boots, the majority of the boot messages refer to devices being detected. A copy of the boot messages are saved to /var/run/dmesg.boot .

Each device has a device name and number. For example, ada0 is the first SATA hard drive, while kbd0 represents the keyboard.

Most devices in FreeBSD must be accessed through special files called device nodes, which are located in /dev .

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

where command is the name of the command to learn about. For example, to learn more about ls(1) , type:

Manual pages are divided into sections which represent the type of topic. In FreeBSD, the following sections are available:

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. To tell man(1) which section to display, specify the section number:

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

If the name of the manual page is unknown, use man -k to search for keywords in the manual page descriptions:

This command displays a list of commands that have the keyword “mail” in their descriptions. This is equivalent to using apropos(1) .

To read the descriptions for all of the commands in /usr/bin , type:

or