Rewritten by Chris Shumway.
3.1 Synopsis
The following chapter will cover the basic commands and functionality of the FreeBSD 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 FreeBSD, then you will definitely want to read through this chapter carefully.
After reading this chapter, you will know:
-
How to use the “virtual consoles” of FreeBSD.
-
How UNIX file permissions work along with understanding file flags in FreeBSD.
-
The default FreeBSD file system layout.
-
The FreeBSD disk organization.
-
How to mount and unmount file systems.
-
What processes, daemons, and signals are.
-
What a shell is, and how to change your default login environment.
-
How to use basic text editors.
-
What devices and device nodes are.
-
What binary format is used under FreeBSD.
-
How to read manual pages for more information.
3.2 Virtual Consoles and Terminals
FreeBSD 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 FreeBSD this way. This section describes what “terminals” and “consoles” are, and how you can use them in FreeBSD.
3.2.1 The Console
If you have not configured FreeBSD 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:.
Local package initialization:.
Additional TCP options:.
Fri Sep 20 13:01:06 EEST 2002
FreeBSD/i386 (pc3.example.org) (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:
FreeBSD/i386 (pc3.example.org) (ttyv0)
This line contains some bits of information about the system you have just booted. You are looking at a “FreeBSD” 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 pc3.example.org, 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 FreeBSD. The next section describes how you can do this.
3.2.2 Logging into FreeBSD
FreeBSD 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 “user” from the rest. In FreeBSD (and all the UNIX-like operating systems), 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”). FreeBSD will ask for these two before allowing a user to run any programs.
Right after FreeBSD 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 FreeBSD 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 FreeBSD.
3.2.3 Multiple Consoles
Running UNIX commands in one console is fine, but FreeBSD 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 FreeBSD can run dozens of programs at the same time. This is where “virtual consoles” can be very helpful.
FreeBSD 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 FreeBSD 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 FreeBSD for switching consoles[3]. You can use Alt-F1, Alt-F2, through Alt-F8 to switch to a different virtual console in FreeBSD.
As you are switching from one console to the next, FreeBSD 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 FreeBSD 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.
3.2.4 The /etc/ttys File
The default configuration of FreeBSD 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 FreeBSD. 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 FreeBSD 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/X11R6/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.
3.2.5 Single User Mode Console
A detailed description of what “single user mode” is can be found in Section 12.6.2. It is worth noting that there is only one console when you are running FreeBSD 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 FreeBSD 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 FreeBSD booting process and the programs involved.
3.2.6 Changing Console Video Modes
The FreeBSD console default video mode may be adjusted to 1024×768, 1280×1024, or any other size supported by your graphics chip and monitor. To use a different video mode, you first must recompile your kernel and include two additional options:
options VESA
options SC_PIXEL_MODE
Once the kernel has been recompiled with these two options, you can then determine what video modes are supported by your hardware by using the vidcontrol(1) utility. To get a list of supported video modes issue the following:
# vidcontrol -i mode
The output of this command is a list of video modes that are supported by your hardware. You can then choose to use a new video mode by passing it to vidcontrol(1) in a root console:
# vidcontrol MODE_279
If the new video mode is acceptable, it can be permanently set on boot by setting it in the /etc/rc.conf file:
allscreens_flags="MODE_279"
3.3 Permissions
FreeBSD, being a direct descendant of BSD UNIX, is based on several key UNIX concepts. The first and most pronounced is that FreeBSD 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? FreeBSD 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.
3.3.1 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 group and “world” write permission on FILE, then it adds the execute permissions for everyone:
% chmod go-w,a+x FILE
3.3.2 FreeBSD File Flags
Contributed by Tom Rhodes.
In addition to file permissions discussed previously, FreeBSD supports the use of “file flags.” These flags add an additional level of security and control over files, but not directories.
These file flags add an additional level of control over files, helping to ensure that in some cases not even the 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
And 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 that administrators read over the chflags(1) and chflags(2) manual pages for more information.
3.3.3 The setuid, setgid, and sticky Permissions
Contributed by Tom Rhodes.
Other than the permissions already discussed, there are three other specific settings that all administrators should know about. They are the setuid, setgid and sticky permissions.
These settings are important for some UNIX operations as they provide functionality not normally granted to normal users. To understand them, the difference between the real user ID and effective user ID must also be noted.
The real user ID is the UID who owns or starts the process. The effective UID is the user ID the process runs as. As an example, the passwd(1) utility runs with the real user ID as the user changing their password; however, to manipulate the password database, it runs as the effective ID of the root user. This is what allows normal users to change their passwords without seeing a “Permission Denied” error.
Note: The nosuid mount(8) option will cause these binaries to silently fail. That is, they will fail to execute without ever alerting the user. That option is also not completely reliable as a nosuid wrapper may be able to circumvent it; according to the mount(8) manual page.
The setuid permission may be set by prefixing a permission set with the number four (4) as shown in the following example:
# chmod 4755 suidexample.sh
The permissions on the suidexample.sh file should now look like the following:
-rwsr-xr-x 1 trhodes trhodes 63 Aug 29 06:36 suidexample.sh
It should be noticeable from this example that an s is now part of the permission set designated for the file owner, replacing the executable bit. This allows utilities which need elevated permissions, such as passwd.
To view this in real time, open two terminals. On one, start the passwd process as a normal user. While it waits for a new password, check the process table and look at the user information of the passwd command.
In terminal A:
Changing local password for trhodes
Old Password:
In terminal B:
# ps aux | grep passwd
trhodes 5232 0.0 0.2 3420 1608 0 R+ 2:10AM 0:00.00 grep passwd
root 5211 0.0 0.2 3620 1724 2 I+ 2:09AM 0:00.01 passwd
As stated above, the passwd is run by a normal user, but is using the effective UID of root.
The setgid permission performs the same function as the setuid permission; except that it alters the group settings. When an application or utility is ran with this setting, it will be granted the permissions based on the group that owns the file, not the user who started the process.
To set the setgid permission on a file, provide the chmod command with a leading two (2) as in the following example:
# chmod 2755 sgidexample.sh
The new setting may be viewed as before, notice the s is now in the field designated for the group permission settings:
-rwxr-sr-x 1 trhodes trhodes 44 Aug 31 01:49 sgidexample.sh
Note: In these examples, even though the shell script in question is an executable file, it will not run with a different EUID or effective user ID. This is because shell scripts may not access the setuid(2) system calls.
The first two special permission bits we discussed (the setuid and setgid permission bits) may lower system security, by allowing for elevated permissions. There is a third special permission bit that can strengthen the security of a system: the sticky bit.
The sticky bit, when set on a directory, allows file deletion only by the file owner. This permission set is useful to prevent file deletion in public directories, such as /tmp, by users who do not own the file. To utilize this permission, prefix the permission with a one (1). For example:
# chmod 1777 /tmp
Now, it is possible to see the effect by using the ls command:
# ls -al / | grep tmp
drwxrwxrwt 10 root wheel 512 Aug 31 01:49 tmp
The sticky bit permission is distinguishable from the t at the very end of the set.
3.4 Directory Structure
The FreeBSD 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 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 Section 3.5. 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 Section 3.6.1.
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).
/rescue/
Statically linked programs for emergency recovery; see rescue(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 using the tmpmfs-related variables of rc.conf(5) (or with an entry in /etc/fstab; see mdmfs(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. Also used as the default destination for the FreeBSD ports framework. Within /usr/local, the general layout sketched out by hier(7) for /usr should be used. Exceptions are the man directory, which is directly under /usr/local rather than under /usr/local/share, and the ports documentation is in share/doc/port.
/usr/obj/
Architecture-specific target tree produced by building the /usr/src tree.
/usr/ports
The FreeBSD Ports Collection (optional).
/usr/sbin/
System daemons & system utilities (executed by users).
/usr/share/
Architecture-independent files.
/usr/src/
BSD and/or local source files.
/usr/X11R6/
X11R6 distribution executables, libraries, etc (optional).
/var/
Multi-purpose log, temporary, transient, and spool files. A memory-based file system is sometimes mounted at /var. This can be automated using the varmfs-related variables of rc.conf(5) (or with an entry in /etc/fstab; see mdmfs(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.
3.5 Disk Organization
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 (.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 uses \ to separate file and directory names, while Mac OS® uses :.
FreeBSD does not use drive letters, or other drive names in the path. You would not write c:/foo/bar/readme.txt on FreeBSD.
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 FreeBSD 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.
This is not normally something you need to concern yourself with. Typically you create file systems when installing FreeBSD 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
-
Different file systems can have different mount options. For example, with careful planning, the root file system can be mounted read-only, making it impossible for you to inadvertently delete or edit a critical file. Separating user-writable file systems, such as /home, from other file systems also allows them to be mounted nosuid; this option prevents the suid/guid bits on executables stored on the file system from taking effect, possibly improving security.
-
FreeBSD automatically optimizes the layout of files on a file system, depending on how the file system is being used. So a file system that contains many small files that are written frequently will have a different optimization to one that contains fewer, larger files. By having one big file system this optimization breaks down.
-
FreeBSD’s file systems are very robust should you lose power. However, a power loss at a critical point could still damage the structure of the file system. By splitting your data over multiple file systems it is more likely that the system will still come up, making it easier for you to restore from backup as necessary.
Benefit of a Single File System
-
File systems are a fixed size. If you create a file system when you install FreeBSD and give it a specific size, you may later discover that you need to make the partition bigger. This is not easily accomplished without backing up, recreating the file system with the new size, and then restoring the backed up data.
Important: FreeBSD features the growfs(8) command, which makes it possible to increase the size of file system on the fly, removing this limitation.
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. Swap space provides FreeBSD with 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.
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.
d
Partition d used to have a special meaning associated with it, although that is now gone and d may work as any normal partition.
Each partition-that-contains-a-file-system is stored in what FreeBSD calls a slice. Slice is FreeBSD’s term for what the common call partitions, and again, this is because of FreeBSD’s UNIX background. Slices are numbered, starting at 1, through to 4.
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 you can have logical slices inside physical slices of the appropriate type. These extended slices are numbered starting at 5, so “ad0s5” is the first extended slice on the first IDE 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”. “ad1s3e” is the fifth partition in the third slice of the second IDE 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 that you will see are listed in Table 3-1.
When referring to a partition FreeBSD requires that you also name the slice and disk that contains the partition, and when referring to a slice you must also refer to the disk name. Thus, you refer to a partition by listing the disk name, s, the slice number, and then the partition letter. Examples are shown in Example 3-1.
Example 3-2 shows a conceptual model of the disk layout that should help make things clearer.
In order to install FreeBSD you must first configure the disk slices, then create partitions within the slice you will use for FreeBSD, and then create a file system (or swap space) in each partition, and decide where that file system will be mounted.
Table 3-1. Disk Device Codes
Code
Meaning
ad
ATAPI (IDE) disk
da
SCSI direct access disk
acd
ATAPI (IDE) CDROM
cd
SCSI CDROM
fd
Floppy disk
Example 3-1. Sample Disk, Slice, and Partition Names
Name
Meaning
ad0s1a
The first partition (a) on the first slice (s1) on the first IDE disk (ad0).
da1s2e
The fifth partition (e) on the second slice (s2) on the second SCSI disk (da1).
Example 3-2. Conceptual Model of a Disk
This diagram shows FreeBSD’s view of the first IDE disk attached to the system. Assume that the disk is 4 GB in size, and contains two 2 GB slices (MS-DOS partitions). The first slice contains a MS-DOS disk, C:, and the second slice contains a FreeBSD installation. This example FreeBSD installation has three data partitions, and a swap partition.
The three partitions will each hold a file system. Partition a will be used for the root file system, e for the /var directory hierarchy, and f for the /usr directory hierarchy.
3.6 Mounting and Unmounting File Systems
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, or CDROM drives.
3.6.1 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
- device
-
A device name (which should exist), as explained in Section 18.2.
- mount-point
-
A directory (which should exist), on which to mount the file system.
- fstype
-
The file system type to pass to mount(8). The default FreeBSD file system is ufs.
- options
-
Either rw for read-write file systems, or ro for read-only file systems, followed by any other options that may be needed. A common option is noauto for file systems not normally mounted during the boot sequence. Other options are listed in the mount(8) manual page.
- dumpfreq
-
This is used by dump(8) to determine which file systems require dumping. If the field is missing, a value of zero is assumed.
- passno
-
This determines the order in which file systems should be checked. File systems that should be skipped should have their passno set to zero. The root file system (which needs to be checked before everything else) should have its passno set to one, and other file systems’ passno should be set to values greater than one. If more than one file systems have the same passno then fsck(8) will attempt to check file systems in parallel if possible.
Consult the fstab(5) manual page for more information on the format of the /etc/fstab file and the options it contains.
3.6.2 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
There are plenty of options, as mentioned in the mount(8) manual page, but the most common are:
Mount Options
-a-
Mount all the file systems listed in /etc/fstab. Except those marked as “noauto”, excluded by the -t flag, or those that are already mounted.
-d-
Do everything except for the actual mount system call. This option is useful in conjunction with the -v flag to determine what mount(8) is actually trying to do.
-f-
Force the mount of an unclean file system (dangerous), or forces the revocation of write access when downgrading a file system’s mount status from read-write to read-only.
-r-
Mount the file system read-only. This is identical to using the ro (rdonly for FreeBSD versions older than 5.2) argument to the -o option.
-t fstype-
Mount the given file system as the given file system type, or mount only file systems of the given type, if given the -a option.
“ufs” is the default file system type.
-u-
Update mount options on the file system.
-v-
Be verbose.
-w-
Mount the file system read-write.
The -o option takes a comma-separated list of the options, including the following:
- noexec
-
Do not allow execution of binaries on this file system. This is also a useful security option.
- nosuid
-
Do not interpret setuid or setgid flags on the file system. This is also a useful security option.
3.6.3 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.
3.7 Processes
FreeBSD 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 FreeBSD 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 (a PID is not reassigned if it is already in use). 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 for each process, 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.
3.8 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 BSD mascot has, for a long time, been 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”. BIND is the Berkeley Internet Name Domain, but 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. One way to do so is to send it (or any other running process), what is known as 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.
FreeBSD 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, FreeBSD 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 FreeBSD will stop that process there and then[4].
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.
-
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 appear in this output. This is because of the way ps(1) has to find the list of running processes.
-
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.
3.9 Shells
In FreeBSD, 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 with everyday tasks such as file management, file globbing, command line editing, command macros, and environment variables. FreeBSD comes with a set of shells, such as sh, the Bourne Shell, and tcsh, the improved C-shell. Many other shells are available from the FreeBSD Ports Collection, 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 type of 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., FreeBSD.
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/local/bin/emacs:
% setenv EDITOR /usr/local/bin/emacs
Under Bourne shells:
% export EDITOR="/usr/local/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.
3.9.1 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/local/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 ports collection, 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.
3.10 Text Editors
A lot of configuration in FreeBSD is done by editing text files. Because of this, it would be 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.
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.
FreeBSD 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 FreeBSD Ports Collection (editors/emacs and editors/vim). 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.
Many applications which modify files or require typed input will automatically open a text editor. To alter the default editor used, set the EDITOR environment variable. See shells section for more details.
3.11 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 FreeBSD boots, the majority of what FreeBSD 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.
3.11.1 Creating Device Nodes
When adding a new device to your system, or compiling in support for additional devices, new device nodes must be created.
3.11.1.1 DEVFS (DEVice File System)
The device file system, or DEVFS, provides access to kernel’s device namespace in the global file system namespace. Instead of having to create and modify device nodes, DEVFS maintains this particular file system for you.
See the devfs(5) manual page for more information.
3.12 Binary Formats
To understand why FreeBSD uses the elf(5) format, you must first know a little about the three currently “dominant” executable formats for UNIX:
-
a.out(5)
The oldest and “classic” UNIX object format. It uses a short and compact header with a magic number at the beginning that is often used to characterize the format (see a.out(5) for more details). It contains three loaded segments: .text, .data, and .bss plus a symbol table and a string table.
-
COFF
The SVR3 object format. The header now comprises a section table, so you can have more than just .text, .data, and .bss sections.
-
elf(5)
The successor to COFF, featuring multiple sections and 32-bit or 64-bit possible values. One major drawback: ELF was also designed with the assumption that there would be only one ABI per system architecture. That assumption is actually quite incorrect, and not even in the commercial SYSV world (which has at least three ABIs: SVR4, Solaris, SCO) does it hold true.
FreeBSD tries to work around this problem somewhat by providing a utility for branding a known ELF executable with information about the ABI it is compliant with. See the manual page for brandelf(1) for more information.
FreeBSD comes from the “classic” camp and used the a.out(5) format, a technology tried and proven through many generations of BSD releases, until the beginning of the 3.X branch. Though it was possible to build and run native ELF binaries (and kernels) on a FreeBSD system for some time before that, FreeBSD initially resisted the “push” to switch to ELF as the default format. Why? Well, when the Linux camp made their painful transition to ELF, it was not so much to flee the a.out executable format as it was their inflexible jump-table based shared library mechanism, which made the construction of shared libraries very difficult for vendors and developers alike. Since the ELF tools available offered a solution to the shared library problem and were generally seen as “the way forward” anyway, the migration cost was accepted as necessary and the transition made. FreeBSD’s shared library mechanism is based more closely on Sun’s SunOS™ style shared library mechanism and, as such, is very easy to use.
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.
However, as time passed, the build tools that FreeBSD derived their build tools from (the assembler and loader especially) evolved in two parallel trees. The FreeBSD tree added shared libraries and fixed some bugs. The GNU folks that originally wrote these programs rewrote them and added simpler support for building cross compilers, plugging in different formats at will, and so on. Since many people wanted to build cross compilers targeting FreeBSD, they were out of luck since the older sources that FreeBSD had for as and ld were not up to the task. The new GNU tools chain (binutils) does support cross compiling, ELF, shared libraries, C++ extensions, etc. In addition, many vendors are releasing ELF binaries, and it is a good thing for FreeBSD to run them.
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. In time support for a.out will be moved out of the GENERIC kernel, and eventually removed from the kernel once the need to run legacy a.out programs is past.
3.13 For More Information
3.13.1 Manual Pages
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 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:
-
User commands.
-
System calls and error numbers.
-
Functions in the C libraries.
-
Device drivers.
-
File formats.
-
Games and other diversions.
-
Miscellaneous information.
-
System maintenance and operation commands.
-
Kernel developers.
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.
3.13.2 GNU Info Files
FreeBSD 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 ?.
Tags:
account,
Apache,
archive,
backup,
bsd,
catch,
cron,
database,
domain,
email,
freebsd,
FreeBSD Handbook,
inetd,
manage,
password,
raw,
sendmail,
software,
xen
Related posts
FreeBSD Handbook account, Apache, archive, backup, bsd, catch, cron, database, domain, email, freebsd, inetd, manage, password, raw, sendmail, software, xen
