The QNX Neutrino operating system doesn't prescribe a specific layout of the filesystem hierarchy,
and a system designer is generally free to structure files in a way that fits the goals of the system.
For example, a multiuser system that's built around generic open-source components may benefit from following
the traditional UNIX filesystem layout (see
http://www.pathname.com).
On the other hand, a secure embedded system may be better off with a layout that avoids union paths
(i.e., any path serviced by more than one resource manager) and where some files are restricted to read-only,
verified, and potentially encrypted filesystems.
The layout of files in a QNX Neutrino system is primarily determined by the following:
- the mountpoint of each resource manager (often referred to as the "attach point")
- the relative path for each file serviced by the resource manager
Filesystem resource managers, including the one that provides the main image filesystem (IFS),
can be mounted at any point in the path space.
The IFS is mounted at / by default and prepends the prefix proc/boot
to all objects in the IFS.
This has the effect that the procfs (/proc resource manager) is always questioned
first for any file that starts with /proc/boot from the IFS, which affects performance slightly.
You can avoid this issue by using the [prefix=""] and [mount="/ifs"]
options in your
mkifs
buildfile to mount the IFS at /ifs instead.
When you're populating a filesystem that can be mounted anywhere, avoid absolute paths and any assumptions
as to where the filesystem is mounted.
For example, the path lib/libfoo.so in a Power-Safe filesystem can become
/lib/libfoo.so if the filesystem is mounted at the root of the path space,
or /fs/qnx6/lib/libfoo.so if it's mounted at /fs/qnx6.
The system's path manager ensures that requests for this path are routed to the correct resource manager.
Many device-specific resource managers (unlike filesystem resource managers) hard-code their mountpoints,
typically under /dev.
This is rarely a requirement, though, and if you find that a device resource manager conflicts with the layout
of your system, you may wish to contact the provider of the resource manager so that they can change that
(or, better yet, let you specify the mountpoint via a command-line option or an environment variable).
Nevertheless, there are a few paths that must exist in a QNX Neutrino system:
- /usr/lib/ldqnx.so.2 or /usr/lib/ldqnx-64.so.2
- The runtime linker (also known as the dynamic linker).
This path is hard-coded in any QNX Neutrino executable.
- /.boot (x86_64 only)
- A directory that contains any IFS binaries and is required by BIOS-based systems.
The rest of this section describes the QNX Neutrino version of the traditional UNIX layout.
/bin
The /bin directory contains binaries of essential utilities,
such as
chmod, ls, and ksh.
To display basic utility syntax, type
use utilityname
from the command line.
For more information, see
use
in the Utilities Reference.
/dev
The /dev directory belongs to the process manager and contains device files,
possibly including:
- /dev/cdn
- CD-ROM block devices; see
devb-*
in the Utilities Reference for driver information.
- /dev/conn
- Text mode console TTY device; see
devc-con
in the Utilities Reference.
- /dev/console
- The device that's used for diagnostic log messages; on a full x86 system, this
is a write-only device managed by the system logger,
slogger2.
Buildfiles for embedded systems may configure a link from this path to
another device, such as a serial port. See slogger2 in the
Utilities Reference.
- /dev/hdn
- Hard disk block devices; data representing an entire drive, spanning all partitions; see
devb-*
in the Utilities Reference.
- /dev/hdntn
- Hard disk partition block devices; the data in these devices is a subset of that
represented by the corresponding hdn file; see
devb-*
in the Utilities Reference.
- /dev/mem
- A device that represents all physical memory.
- /dev/mq and /dev/mqueue
- A pathname space where entries for message queues appear; for more information, see
mq
and
mqueue
in the Utilities Reference.
- /dev/null
- A “bit bucket” that you can direct data to. The data is discarded.
- /dev/pci
- Adopted by the PCI server on the machine, this device lets programs communicate
with the PCI server. See
pci-*
in the Utilities Reference.
- /dev/pipe
- Adopted by the
pipe
manager. The presence of this file tells other programs (such as a
startup script built into an OS image) that the Pipe manager is successfully running.
- /dev/pty[p-zP-T][0-9a-f]
- The control side of a pseudo-terminal device pair. Pseudo-ttys are named with a
letter (p–z or P–T) followed by a hexadecimal digit, making it
possible to have up to 256 devices. See
devc-pty
in the Utilities Reference.
- /dev/random
- Read from this device to obtain random data; see
random
in the Utilities Reference.
- /dev/sem
- A pathname space where entries for named semaphores appear.
- /dev/sern
- Serial ports. See
stty
for configuration, and
devc-ser*
for driver details in the Utilities Reference.
- /dev/shmem/
- Contains files representing shared memory regions on the system (also sometimes
used for generic memory-mapped files). For more information, see the description of the
RAM “filesystem”
in Working with Filesystems.
- /dev/socket/
- This directory is owned and managed through the TCP/IP stack, which is included in
io-pkt*.
This directory contains pathnames through which applications interact with the stack.
For more information, see the
TCP/IP Networking chapter in this guide.
- /dev/text
- This file is managed by
procnto.
Text written to this device is output through debug output routines
encoded in the startup code for your system, so the actual result varies from board to board.
On a standard PC, the default is to write to the PC console.
For more information, see
startup-*
in the Utilities Reference.
- /dev/tty
- A virtual device owned by the process manager
(procnto)
that resolves to the controlling terminal device associated with the
session of any process that opens the file. This is useful for programs that may
have closed their standard input, standard output, or standard error, and later
wish to write to the terminal device.
- /dev/tty[p-zP-T][0-9a-f]
- The slave side of the corresponding
/dev/pty[p-zP-T][0-9a-f] file.
The program being controlled typically uses one of these files for its standard input,
standard output, and standard error.
- /dev/zero
- Supplies an endless stream of bytes having a value of zero.
/etc
The /etc directory contains host-specific system files and programs used for
administration and configuration, including:
- /etc/bootptab
- Network boot protocol server configuration file. See
/etc/bootptab
in the Utilities Reference.
- /etc/config/
- A directory that contains system-configuration files, such as the
ttys file that
tinit
uses to configure terminal devices.
- /etc/default/
- A directory that contains default configuration files, primarily for TCP/IP facilities.
- /etc/dhcpd.conf
- Dynamic Host Configuration Protocol configuration; see
/etc/dhcpd.conf
in the Utilities Reference.
- /etc/ftpd.conf
- Configuration options for
ftpd
that apply once you've authenticated your connection. See
../../com.qnx.doc.neutrino.utilities/topic/f/ftpd.conf.html
in the Utilities Reference.
- /etc/ftpusers
- Defines users who may access the machine via the File Transfer Protocol. See
/etc/ftpusers
in the Utilities Reference.
- /etc/group
- User account group definitions; see
Managing User Accounts.
- /etc/hosts
- Network hostname lookup database; see also
/etc/nsswitch.conf and
/etc/resolv.conf, below. See
/etc/hosts
in the Utilities Reference.
- /etc/inetd.conf
- Internet super-server configuration file that defines Internet services that
inetd
starts and stops dynamically as needed.
Note:
The descriptions in the default version of this file are commented out;
uncomment the ones that you want to use. See
/etc/inetd.conf
in the
Utilities Reference.
- /etc/motd
- Contains an ASCII message of the day that may be displayed when users log in, as
long as /etc/profile is configured to display it.
The default /etc/profile displays this
file only if the /etc/motd file is more recent than the
time you last logged in to the system, as determined by the time your
$HOME/.lastlogin file was last modified. For
more information, see the description of
/etc/profile
in Configuring Your Environment.
- /etc/networks
- Network name database file. For more information, see
/etc/networks
in the Utilities Reference.
- /etc/nsswitch.conf
- Name-service switch configuration file. For more information, see
/etc/nsswitch.conf
in the Utilities Reference.
- /etc/opasswd
- Backup of /etc/passwd file before its last change via the
passwd
utility.
See the
Managing User Accounts
chapter.
- /etc/oshadow
- Backup of /etc/shadow file before its last change via the
passwd
utility.
Managing User Accounts.
- /etc/passwd
- This file defines login accounts.
See the chapter
Logging In, Logging Out, and Shutting Down, as well as
Managing User Accounts
for more details; also see
passwd,
login
in the Utilities Reference.
- /etc/profile
- The startup profile script executed by the shell when you log in; it's executed before
$HOME/.profile. See
Configuring Your Environment.
- /etc/profile.d/
- A directory where the default /etc/profile script looks for
scripts to run when any user logs in. The /etc/profile
script runs each script in this directory that matches
*.$(SHELL##*/}. For example, if the value of the
SHELL environment variable is /bin/sh,
the script runs the scripts that match *.sh.
- /etc/resolv.conf
- Resolver configuration file; see also /etc/hosts, above.
See
/etc/resolv.conf
in the Utilities Reference.
- /etc/skel/
- A directory that holds the default version of .profile.
When you add a new user to the system, this file is copied to the user's home
directory. For more information, see the description of
/etc/default/passwd in the documentation for
passwd,
and the description of
.profile
in Configuring Your Environment.
/home
The home directories of regular users are found here.
The name of your home directory is often the same as your user name.
You can create whatever directory structure you need inside your home directory.
/lib
This directory contains essential shared libraries that programs need in order to run
(filename.so),
as well as static libraries used
during development. See also /usr/lib and
/usr/local/lib.
The /lib directory includes:
- /lib/dll/
- Contains additional shared libraries that implement OS drivers and
services, such as drivers, filesystem managers, and so on.
For some examples of how shared libraries are used for certain types
of drivers and services, see
Filesystems,
Native Networking (Qnet),
and
TCP/IP Networking
in the System Architecture guide.
For details about specific shared objects in the
/lib/dll directory, see their respective entries in the
Utilities Reference.
/proc
Owned by the process manager (procnto),
this virtual directory can give you information about processes and
pathname-space configuration.
The /proc directory contains a subdirectory for each process;
the process ID is used as the name of the directory.
Each of these directories contains entries that you can (with the appropriate permission) use to access
the process's address space, control its threads, and so on.
Various utilities use this entry to get information about a
process.
For more information, see
“Controlling processes via the /proc filesystem”
in the Processes chapter of the QNX Neutrino Programmer's Guide,
and the
/proc Filesystem
appendix of The QNX Neutrino Cookbook.
The /proc directory also includes:
- /proc/boot/
- The image filesystem that comprises the boot image.
For more information, see
OS Images
in Building Embedded Systems.
- /proc/dumper
- A special entry that receives notification when a process terminates
abnormally.
The
dumper
utility creates this entry.
- /proc/mount/
- Pathname-space mountpoints.
Note:
If you list the contents of the /proc directory,
/proc/mount doesn't show up, but you can list the
contents of /proc/mount.
For more information, see
“The /proc/mount directory”
in the /proc Filesystem appendix of The QNX Neutrino Cookbook.
- /proc/qnetstats
- If you're using Transparent Distributed Processing (TDP), the
lsm-qnet.so
module places a qnetstats entry in /proc.
If you open this name and read from it, the Qnet resource manager code
responds with the current statistics for Qnet.
- /proc/self/
- The address space for yourself (i.e., for the process that's making the query).
/root
The /root directory is the home directory for the
root user.
/sbin
This directory contains essential system binaries, including:
- drivers (e.g.,
devb*,
devc*,
devf*,
devu*)
- initialization programs
- configuration utilities (e.g.,
ifconfig)
and repair utilities (e.g.,
chkqnx6fs,
chkdosfs)
- managers (e.g.,
io-pkt*,
mqueue,
pipe)
/tmp
This directory contains temporary files.
Programs are supposed to remove their temporary files after using them,
but sometimes they don't, either due to poor coding or abnormal termination.
You can periodically clean out extraneous temporary files when your system is idle.
/usr
The /usr directory is a secondary file hierarchy that contains shareable, read-only data.
It might include the following:
- /usr/bin/
- A directory that contains most user commands.
Examples include
diff,
errno,
and
wc.
- /usr/lib/
- Object files, libraries, and internal binaries that you shouldn't execute
directly or in scripts. You'll link against these libraries if you write any programs.
- /usr/libexec/
- A directory that could contain system daemons and system utilities; in general,
these are run only by other programs.
- /usr/local/
- A directory where the system administrator can install software locally. It's
initially empty.
- /usr/sbin/
- Nonessential system binaries, such as
cron,
dumper,
and
nicinfo.
- /usr/share/
- Data that's independent of the architecture, such as icons, backdrops, and various
gawk
programs.
/var
The /var directory contains variable data files, including cache files, lock files,
log files, and so on.
- /var/pps
- The directory where the Persistent Publish/Subscribe manager,
pps,
stores (“persists”) its state on shutdown.