the Linux file tree
(Written by Paul Cobbaut, https://github.com/paulcobbaut/, with contributions by: Alex M. Schapelle, https://github.com/zero-pytagoras/, Serge Van Ginderachter, https://github.com/srgvg/)
This chapter takes a look at the most common directories in the
Linux file tree. It also shows that on Unix everything is a file.
filesystem hierarchy standard
Many Linux distributions partially follow the
Filesystem Hierarchy Standard. The FHS may help make
more Unix/Linux file system trees conform better in the future. The
FHS is available online at
http://www.pathname.com/fhs/ where we read: \"The
filesystem hierarchy standard has been designed to be used by Unix
distribution developers, package developers, and system implementers.
However, it is primarily intended to be a reference and is not a
tutorial on how to manage a Unix filesystem or directory hierarchy.\"
man hier
There are some differences in the filesystems between
Linux distributions. For help about your machine, enter
man hier to find information about the file system
hierarchy. This manual will explain the directory structure on your
computer.
the root directory /
All Linux systems have a directory structure that starts at the
root directory. The root directory is represented by a
forward slash, like this: /. Everything that exists on
your Linux system can be found below this root directory. Let\'s take a
brief look at the contents of the root directory.
[student@linux ~]$ ls /
bin dev home media mnt proc sbin srv tftpboot usr
boot etc lib misc opt root selinux sys tmp var
binary directories
Binaries are files that contain compiled source code (or machine
code). Binaries can be executed on the computer. Sometimes binaries
are called executables.
/bin
The /bin directory contains binaries for
use by all users. According to the FHS the /bin directory should
contain /bin/cat and /bin/date (among
others).
In the screenshot below you see common Unix/Linux commands like cat, cp, cpio, date, dd, echo, grep, and so on. Many of these will be covered in this book.
student@linux:~$ ls /bin
archdetect egrep mt setupcon
autopartition false mt-gnu sh
bash fgconsole mv sh.distrib
bunzip2 fgrep nano sleep
bzcat fuser nc stralign
bzcmp fusermount nc.traditional stty
bzdiff get_mountoptions netcat su
bzegrep grep netstat sync
bzexe gunzip ntfs-3g sysfs
bzfgrep gzexe ntfs-3g.probe tailf
bzgrep gzip parted_devices tar
bzip2 hostname parted_server tempfile
bzip2recover hw-detect partman touch
bzless ip partman-commit true
bzmore kbd_mode perform_recipe ulockmgr
cat kill pidof umount
...
other /bin directories
You can find a /bin subdirectory in many other directories. A user
named serena could put her own programs in /home/serena/bin.
Some applications, often when installed directly from source will put
themselves in /opt. A samba server installation can use
/opt/samba/bin to store its binaries.
/sbin
/sbin contains binaries to configure the operating
system. Many of the system binaries require root
privilege to perform certain tasks.
Below a screenshot containing system binaries to change the ip
address, partition a disk and create an ext4 file system.
student@linux:~$ ls -l /sbin/ifconfig /sbin/fdisk /sbin/mkfs.ext4
-rwxr-xr-x 1 root root 97172 2011-02-02 09:56 /sbin/fdisk
-rwxr-xr-x 1 root root 65708 2010-07-02 09:27 /sbin/ifconfig
-rwxr-xr-x 5 root root 55140 2010-08-18 18:01 /sbin/mkfs.ext4
/lib
Binaries found in /bin and /sbin often use shared libraries
located in /lib. Below is a screenshot of the partial
contents of /lib.
student@linux:~$ ls /lib/libc*
/lib/libc-2.5.so /lib/libcfont.so.0.0.0 /lib/libcom_err.so.2.1
/lib/libcap.so.1 /lib/libcidn-2.5.so /lib/libconsole.so.0
/lib/libcap.so.1.10 /lib/libcidn.so.1 /lib/libconsole.so.0.0.0
/lib/libcfont.so.0 /lib/libcom_err.so.2 /lib/libcrypt-2.5.so
/lib/modules
Typically, the Linux kernel loads kernel modules from
/lib/modules/$kernel-version/. This directory is
discussed in detail in the Linux kernel chapter.
/lib32 and /lib64
We currently are in a transition between 32-bit and 64-bit systems.
Therefore, you may encounter directories named /lib32
and /lib64 which clarify the register size used during
compilation time of the libraries. A 64-bit computer may have some
32-bit binaries and libraries for compatibility with legacy
applications. This screenshot uses the file utility to
demonstrate the difference.
student@linux:~$ file /lib32/libc-2.5.so
/lib32/libc-2.5.so: ELF 32-bit LSB shared object, Intel 80386, \
version 1 (SYSV), for GNU/Linux 2.6.0, stripped
student@linux:~$ file /lib64/libcap.so.1.10
/lib64/libcap.so.1.10: ELF 64-bit LSB shared object, AMD x86-64, \
version 1 (SYSV), stripped
The ELF (Executable and Linkable Format) is used in
almost every Unix-like operating system since System V.
/opt
The purpose of /opt is to store optional software. In many cases
this is software from outside the distribution repository. You may find
an empty /opt directory on many systems.
A large package can install all its files in /bin, /lib, /etc
subdirectories within /opt/$packagename/. If for example the package
is called wp, then it installs in /opt/wp, putting binaries in
/opt/wp/bin and manpages in /opt/wp/man.
configuration directories
/boot
The /boot directory contains all files needed to boot
the computer. These files don\'t change very often. On Linux systems you
typically find the /boot/grub directory here.
/boot/grub contains /boot/grub/grub.cfg (older systems
may still have /boot/grub/grub.conf) which defines the
boot menu that is displayed before the kernel starts.
/etc
All of the machine-specific configuration files should be located in
/etc. Historically /etc stood for etcetera, today
people often use the Editable Text Configuration backronym.
Many times the name of a configuration files is the same as the
application, daemon, or protocol with .conf added as the extension.
student@linux:~$ ls /etc/*.conf
/etc/adduser.conf /etc/ld.so.conf /etc/scrollkeeper.conf
/etc/brltty.conf /etc/lftp.conf /etc/sysctl.conf
/etc/ccertificates.conf /etc/libao.conf /etc/syslog.conf
/etc/cvs-cron.conf /etc/logrotate.conf /etc/ucf.conf
/etc/ddclient.conf /etc/ltrace.conf /etc/uniconf.conf
/etc/debconf.conf /etc/mke2fs.conf /etc/updatedb.conf
/etc/deluser.conf /etc/netscsid.conf /etc/usplash.conf
/etc/fdmount.conf /etc/nsswitch.conf /etc/uswsusp.conf
/etc/hdparm.conf /etc/pam.conf /etc/vnc.conf
/etc/host.conf /etc/pnm2ppa.conf /etc/wodim.conf
/etc/inetd.conf /etc/povray.conf /etc/wvdial.conf
/etc/kernel-img.conf /etc/resolv.conf
student@linux:~$
There is much more to be found in /etc.
/etc/init.d/
A lot of Unix/Linux distributions have an /etc/init.d
directory that contains scripts to start and stop daemons. This
directory could disappear as Linux migrates to systems that replace the
old init way of starting all daemons.
/etc/X11/
The graphical display (aka X Window System or just
X) is driven by software from the X.org foundation. The
configuration file for your graphical display is
/etc/X11/xorg.conf.
/etc/skel/
The skeleton directory /etc/skel is
copied to the home directory of a newly created user. It usually
contains hidden files like a .bashrc script.
/etc/sysconfig/
This directory, which is not mentioned in the FHS, contains a lot of
Red Hat Enterprise Linux configuration files. We will discuss some of
them in greater detail. The screenshot below is the
/etc/sysconfig directory from RHELv8u4 with everything
installed.
student@linux:~$ ls /etc/sysconfig/
apmd firstboot irda network saslauthd
apm-scripts grub irqbalance networking selinux
authconfig hidd keyboard ntpd spamassassin
autofs httpd kudzu openib.conf squid
bluetooth hwconf lm_sensors pand syslog
clock i18n mouse pcmcia sys-config-sec
console init mouse.B pgsql sys-config-users
crond installinfo named prelink sys-logviewer
desktop ipmi netdump rawdevices tux
diskdump iptables netdump_id_dsa rhn vncservers
dund iptables-cfg netdump_id_dsa.p samba xinetd
student@linux:~$
The file /etc/sysconfig/firstboot tells the Red Hat
Setup Agent not to run at boot time. If you want to run the Red Hat
Setup Agent at the next reboot, then simply remove this file, and run
chkconfig --level 5 firstboot on. The Red Hat Setup
Agent allows you to install the latest updates, create a user account,
join the Red Hat Network and more. It will then create the
/etc/sysconfig/firstboot file again.
student@linux:~$ cat /etc/sysconfig/firstboot
RUN_FIRSTBOOT=NO
The /etc/sysconfig/harddisks file contains some
parameters to tune the hard disks. The file explains itself.
You can see hardware detected by kudzu in
/etc/sysconfig/hwconf. Kudzu is software from Red Hat
for automatic discovery and configuration of hardware.
The keyboard type and keymap table are set in the
/etc/sysconfig/keyboard file. For more console keyboard
information, check the manual pages of keymaps(5),
dumpkeys(1), loadkeys(1) and the
directory /lib/kbd/keymaps/.
root@linux:/etc/sysconfig# cat keyboard
KEYBOARDTYPE="pc"
KEYTABLE="us"
We will discuss networking files in this directory in the networking chapter.
data directories
/home
Users can store personal or project data under /home. It
is common (but not mandatory by the fhs) practice to name the users home
directory after the user name in the format /home/$USERNAME. For
example:
student@linux:~$ ls /home
geert annik sandra paul tom
Besides giving every user (or every project or group) a location to store personal files, the home directory of a user also serves as a location to store the user profile. A typical Unix user profile contains many hidden files (files whose file name starts with a dot). The hidden files of the Unix user profiles contain settings specific for that user.
student@linux:~$ ls -d /home/paul/.*
/home/paul/. /home/paul/.bash_profile /home/paul/.ssh
/home/paul/.. /home/paul/.bashrc /home/paul/.viminfo
/home/paul/.bash_history /home/paul/.lesshst
/root
On many systems /root is the default location for
personal data and profile of the root user. If it does not exist by
default, then some administrators create it.
/srv
You may use /srv for data that is
served by your system. The FHS allows locating cvs, rsync, ftp and www
data in this location. The FHS also approves administrative naming in
/srv, like /srv/project55/ftp and /srv/sales/www.
On Sun Solaris (or Oracle Solaris) /export is used for
this purpose.
/media
The /media directory serves as a mount point for
removable media devices such as CD-ROM\'s, digital cameras, and
various usb-attached devices. Since /media is rather new in the Unix
world, you could very well encounter systems running without this
directory. Solaris 9 does not have it, Solaris 10 does. Most Linux
distributions today mount all removable media in /media.
student@linux:~$ ls /media/
cdrom cdrom0 usbdisk
/mnt
The /mnt directory should be empty and should only be used for
temporary mount points (according to the FHS).
Unix and Linux administrators used to create many directories here, like
/mnt/something/. You likely will encounter many systems with more than
one directory created and/or mounted inside /mnt to be used for
various local and remote filesystems.
/tmp
Applications and users should use /tmp to store
temporary data when needed. Data stored in /tmp may use either disk
space or RAM. Both of which are managed by the operating system. Never
use /tmp to store data that is important or which you wish to archive.
in memory directories
/dev
Device files in /dev appear to be ordinary files, but
are not actually located on the hard disk. The /dev directory is
populated with files as the kernel is recognising hardware.
common physical devices
Common hardware such as hard disk devices are represented by device
files in /dev. Below a screenshot of SATA device files on a laptop and
then IDE attached drives on a desktop. (The detailed meaning of these
devices will be discussed later.)
#
# SATA or SCSI or USB
#
student@linux:~$ ls /dev/sd*
/dev/sda /dev/sda1 /dev/sda2 /dev/sda3 /dev/sdb /dev/sdb1 /dev/sdb2
#
# IDE or ATAPI
#
student@linux:~$ ls /dev/hd*
/dev/hda /dev/hda1 /dev/hda2 /dev/hdb /dev/hdb1 /dev/hdb2 /dev/hdc
Besides representing physical hardware, some device files are special. These special devices can be very useful.
/dev/tty and /dev/pts
For example, /dev/tty1 represents a terminal or console
attached to the system. (Don\'t break your head on the exact terminology
of \'terminal\' or \'console\', what we mean here is a command line
interface.) When typing commands in a terminal that is part of a
graphical interface like Gnome or KDE, then your terminal will be
represented as /dev/pts/1 (1 can be another number).
/dev/null
On Linux you will find other special devices such as
/dev/null which can be considered a black hole; it has
unlimited storage, but nothing can be retrieved from it. Technically
speaking, anything written to /dev/null will be discarded. /dev/null can
be useful to discard unwanted output from commands. /dev/null is not a
good location to store your backups ;-).
/proc conversation with the kernel
/proc is another special directory, appearing to be
ordinary files, but not taking up disk space. It is actually a view of
the kernel, or better, what the kernel manages, and is a means to
interact with it directly. /proc is a proc filesystem.
student@linux:~$ mount -t proc
none on /proc type proc (rw)
When listing the /proc directory you will see many numbers (on any Unix) and some interesting files (on Linux)
mul@linux:~$ ls /proc
1 2339 4724 5418 6587 7201 cmdline mounts
10175 2523 4729 5421 6596 7204 cpuinfo mtrr
10211 2783 4741 5658 6599 7206 crypto net
10239 2975 4873 5661 6638 7214 devices pagetypeinfo
141 29775 4874 5665 6652 7216 diskstats partitions
15045 29792 4878 5927 6719 7218 dma sched_debug
1519 2997 4879 6 6736 7223 driver scsi
1548 3 4881 6032 6737 7224 execdomains self
1551 30228 4882 6033 6755 7227 fb slabinfo
1554 3069 5 6145 6762 7260 filesystems stat
1557 31422 5073 6298 6774 7267 fs swaps
1606 3149 5147 6414 6816 7275 ide sys
180 31507 5203 6418 6991 7282 interrupts sysrq-trigger
181 3189 5206 6419 6993 7298 iomem sysvipc
182 3193 5228 6420 6996 7319 ioports timer_list
18898 3246 5272 6421 7157 7330 irq timer_stats
19799 3248 5291 6422 7163 7345 kallsyms tty
19803 3253 5294 6423 7164 7513 kcore uptime
19804 3372 5356 6424 7171 7525 key-users version
1987 4 5370 6425 7175 7529 kmsg version_signature
1989 42 5379 6426 7188 9964 loadavg vmcore
2 45 5380 6430 7189 acpi locks vmnet
20845 4542 5412 6450 7191 asound meminfo vmstat
221 46 5414 6551 7192 buddyinfo misc zoneinfo
2338 4704 5416 6568 7199 bus modules
Let\'s investigate the file properties inside /proc. Looking at the
date and time will display the current date and time showing the files
are constantly updated (a view on the kernel).
student@linux:~$ date
Mon Jan 29 18:06:32 EST 2007
student@linux:~$ ls -al /proc/cpuinfo
-r--r--r-- 1 root root 0 Jan 29 18:06 /proc/cpuinfo
student@linux:~$
student@linux:~$ ...time passes...
student@linux:~$
student@linux:~$ date
Mon Jan 29 18:10:00 EST 2007
student@linux:~$ ls -al /proc/cpuinfo
-r--r--r-- 1 root root 0 Jan 29 18:10 /proc/cpuinfo
Most files in /proc are 0 bytes, yet they contain data--sometimes a lot
of data. You can see this by executing cat on files like
/proc/cpuinfo, which contains information about the CPU.
student@linux:~$ file /proc/cpuinfo
/proc/cpuinfo: empty
student@linux:~$ cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 15
model : 43
model name : AMD Athlon(tm) 64 X2 Dual Core Processor 4600+
stepping : 1
cpu MHz : 2398.628
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge...
bogomips : 4803.54
Just for fun, here is /proc/cpuinfo on a Sun Sunblade 1000...
student@linux:~$ cat /proc/cpuinfo
cpu : TI UltraSparc III (Cheetah)
fpu : UltraSparc III integrated FPU
promlib : Version 3 Revision 2
prom : 4.2.2
type : sun4u
ncpus probed : 2
ncpus active : 2
Cpu0Bogo : 498.68
Cpu0ClkTck : 000000002cb41780
Cpu1Bogo : 498.68
Cpu1ClkTck : 000000002cb41780
MMU Type : Cheetah
State:
CPU0: online
CPU1: online
Most of the files in /proc are read only, some require root privileges,
some files are writable, and many files in /proc/sys are
writable. Let\'s discuss some of the files in /proc.
/proc/interrupts
On the x86 architecture, /proc/interrupts displays the
interrupts.
student@linux:~$ cat /proc/interrupts
CPU0
0: 13876877 IO-APIC-edge timer
1: 15 IO-APIC-edge i8042
8: 1 IO-APIC-edge rtc
9: 0 IO-APIC-level acpi
12: 67 IO-APIC-edge i8042
14: 128 IO-APIC-edge ide0
15: 124320 IO-APIC-edge ide1
169: 111993 IO-APIC-level ioc0
177: 2428 IO-APIC-level eth0
NMI: 0
LOC: 13878037
ERR: 0
MIS: 0
On a machine with two CPU\'s, the file looks like this.
student@linux:~$ cat /proc/interrupts
CPU0 CPU1
0: 860013 0 IO-APIC-edge timer
1: 4533 0 IO-APIC-edge i8042
7: 0 0 IO-APIC-edge parport0
8: 6588227 0 IO-APIC-edge rtc
10: 2314 0 IO-APIC-fasteoi acpi
12: 133 0 IO-APIC-edge i8042
14: 0 0 IO-APIC-edge libata
15: 72269 0 IO-APIC-edge libata
18: 1 0 IO-APIC-fasteoi yenta
19: 115036 0 IO-APIC-fasteoi eth0
20: 126871 0 IO-APIC-fasteoi libata, ohci1394
21: 30204 0 IO-APIC-fasteoi ehci_hcd:usb1, uhci_hcd:usb2
22: 1334 0 IO-APIC-fasteoi saa7133[0], saa7133[0]
24: 234739 0 IO-APIC-fasteoi nvidia
NMI: 72 42
LOC: 860000 859994
ERR: 0
/proc/kcore
The physical memory is represented in /proc/kcore. Do
not try to cat this file, instead use a debugger. The size of
/proc/kcore is the same as your physical memory, plus four bytes.
student@linux:~$ ls -lh /proc/kcore
-r-------- 1 root root 2.0G 2007-01-30 08:57 /proc/kcore
student@linux:~$
/sys Linux 2.6 hot plugging
The /sys directory was created for the Linux 2.6 kernel.
Since 2.6, Linux uses sysfs to support
usb and IEEE 1394
(FireWire) hot plug devices. See the manual pages of
udev(8) (the successor of devfs) and hotplug(8) for more
info (or visit http://linux-hotplug.sourceforge.net/ ).
Basically the /sys directory contains kernel information about
hardware.
/usr Unix System Resources
Although /usr is pronounced like user, remember that it
stands for Unix System Resources. The /usr hierarchy should contain
shareable, read only data. Some people choose to mount /usr as read
only. This can be done from its own partition or from a read only NFS
share (NFS is discussed later).
/usr/bin
The /usr/bin directory contains a lot of commands.
student@linux:~$ ls /usr/bin | wc -l
1395
(On Solaris the /bin directory is a symbolic link to /usr/bin.)
/usr/include
The /usr/include directory contains general use include
files for C.
student@linux:~$ ls /usr/include/
aalib.h expat_config.h math.h search.h
af_vfs.h expat_external.h mcheck.h semaphore.h
aio.h expat.h memory.h setjmp.h
AL fcntl.h menu.h sgtty.h
aliases.h features.h mntent.h shadow.h
...
/usr/lib
The /usr/lib directory contains libraries that are not
directly executed by users or scripts.
student@linux:~$ ls /usr/lib | head -7
4Suite
ao
apt
arj
aspell
avahi
bonobo
/usr/local
The /usr/local directory can be used by an administrator
to install software locally.
student@linux:~$ ls /usr/local/
bin etc games include lib man sbin share src
student@linux:~$ du -sh /usr/local/
128K /usr/local/
/usr/share
The /usr/share directory contains architecture
independent data. As you can see, this is a fairly large directory.
student@linux:~$ ls /usr/share/ | wc -l
263
student@linux:~$ du -sh /usr/share/
1.3G /usr/share/
This directory typically contains /usr/share/man for
manual pages.
student@linux:~$ ls /usr/share/man
cs fr hu it.UTF-8 man2 man6 pl.ISO8859-2 sv
de fr.ISO8859-1 id ja man3 man7 pl.UTF-8 tr
es fr.UTF-8 it ko man4 man8 pt_BR zh_CN
fi gl it.ISO8859-1 man1 man5 pl ru zh_TW
And it contains /usr/share/games for all static game
data (so no high-scores or play logs).
student@linux:~$ ls /usr/share/games/
openttd wesnoth
/usr/src
The /usr/src directory is the recommended location for
kernel source files.
student@linux:~$ ls -l /usr/src/
total 12
drwxr-xr-x 4 root root 4096 2011-02-01 14:43 linux-headers-2.6.26-2-686
drwxr-xr-x 18 root root 4096 2011-02-01 14:43 linux-headers-2.6.26-2-common
drwxr-xr-x 3 root root 4096 2009-10-28 16:01 linux-kbuild-2.6.26
/var variable data
Files that are unpredictable in size, such as log, cache and spool
files, should be located in /var.
/var/log
The /var/log directory serves as a central point to
contain all log files.
[student@linux ~]$ ls /var/log
acpid cron.2 maillog.2 quagga secure.4
amanda cron.3 maillog.3 radius spooler
anaconda.log cron.4 maillog.4 rpmpkgs spooler.1
anaconda.syslog cups mailman rpmpkgs.1 spooler.2
anaconda.xlog dmesg messages rpmpkgs.2 spooler.3
audit exim messages.1 rpmpkgs.3 spooler.4
boot.log gdm messages.2 rpmpkgs.4 squid
boot.log.1 httpd messages.3 sa uucp
boot.log.2 iiim messages.4 samba vbox
boot.log.3 iptraf mysqld.log scrollkeeper.log vmware-tools-guestd
boot.log.4 lastlog news secure wtmp
canna mail pgsql secure.1 wtmp.1
cron maillog ppp secure.2 Xorg.0.log
cron.1 maillog.1 prelink.log secure.3 Xorg.0.log.old
/var/log/messages
A typical first file to check when troubleshooting on Red Hat (and
derivatives) is the /var/log/messages file. By default
this file will contain information on what just happened to the system.
The file is called /var/log/syslog on Debian and Ubuntu.
[root@linux ~]# tail /var/log/messages
Jul 30 05:13:56 anacron: anacron startup succeeded
Jul 30 05:13:56 atd: atd startup succeeded
Jul 30 05:13:57 messagebus: messagebus startup succeeded
Jul 30 05:13:57 cups-config-daemon: cups-config-daemon startup succeeded
Jul 30 05:13:58 haldaemon: haldaemon startup succeeded
Jul 30 05:14:00 fstab-sync[3560]: removed all generated mount points
Jul 30 05:14:01 fstab-sync[3628]: added mount point /media/cdrom for...
Jul 30 05:14:01 fstab-sync[3646]: added mount point /media/floppy for...
Jul 30 05:16:46 sshd(pam_unix)[3662]: session opened for user paul by...
Jul 30 06:06:37 su(pam_unix)[3904]: session opened for user root by paul
/var/cache
The /var/cache directory can contain cache data for
several applications.
student@linux:~$ ls /var/cache/
apt dictionaries-common gdm man software-center
binfmts flashplugin-installer hald pm-utils
cups fontconfig jockey pppconfig
debconf fonts ldconfig samba
/var/spool
The /var/spool directory typically contains spool
directories for mail and cron, but also serves as a parent directory
for other spool files (for example print spool files).
/var/lib
The /var/lib directory contains application state
information.
Red Hat Enterprise Linux for example keeps files pertaining to
rpm in /var/lib/rpm/.
/var/...
/var also contains Process ID files in /var/run (soon
to be replaced with /run) and temporary files that
survive a reboot in /var/tmp and information about file
locks in /var/lock. There will be more examples of
/var usage further in this book.
practice: file system tree
1. Does the file /bin/cat exist ? What about /bin/dd and
/bin/echo. What is the type of these files ?
2. What is the size of the Linux kernel file(s) (vmlinu*) in /boot ?
3. Create a directory \~/test. Then issue the following commands:
cd ~/test
dd if=/dev/zero of=zeroes.txt count=1 bs=100
od zeroes.txt
dd will copy one times (count=1) a block of size 100 bytes (bs=100)
from the file /dev/zero to \~/test/zeroes.txt. Can you describe the
functionality of /dev/zero ?
4. Now issue the following command:
dd if=/dev/random of=random.txt count=1 bs=100 ; od random.txt
dd will copy one times (count=1) a block of size 100 bytes (bs=100)
from the file /dev/random to \~/test/random.txt. Can you describe the
functionality of /dev/random ?
5. Issue the following two commands, and look at the first character of each output line.
ls -l /dev/sd* /dev/hd*
ls -l /dev/tty* /dev/input/mou*
The first ls will show block(b) devices, the second ls shows character(c) devices. Can you tell the difference between block and character devices ?
6. Use cat to display /etc/hosts and /etc/resolv.conf. What is your
idea about the purpose of these files ?
7. Are there any files in /etc/skel/ ? Check also for hidden files.
8. Display /proc/cpuinfo. On what architecture is your Linux running
?
9. Display /proc/interrupts. What is the size of this file ? Where is
this file stored ?
10. Can you enter the /root directory ? Are there (hidden) files ?
11. Are ifconfig, fdisk, parted, shutdown and grub-install present in
/sbin ? Why are these binaries in /sbin and not in /bin ?
12. Is /var/log a file or a directory ? What about /var/spool ?
13. Open two command prompts (Ctrl-Shift-T in gnome-terminal) or
terminals (Ctrl-Alt-F1, Ctrl-Alt-F2, ...) and issue the who am i in
both. Then try to echo a word from one terminal to the other.
14. Read the man page of random and explain the difference between
/dev/random and /dev/urandom.
solution: file system tree
1. Does the file /bin/cat exist ? What about /bin/dd and
/bin/echo. What is the type of these files ?
ls /bin/cat ; file /bin/cat
ls /bin/dd ; file /bin/dd
ls /bin/echo ; file /bin/echo
2. What is the size of the Linux kernel file(s) (vmlinu*) in /boot ?
ls -lh /boot/vm*
3. Create a directory \~/test. Then issue the following commands:
cd ~/test
dd if=/dev/zero of=zeroes.txt count=1 bs=100
od zeroes.txt
dd will copy one times (count=1) a block of size 100 bytes (bs=100)
from the file /dev/zero to \~/test/zeroes.txt. Can you describe the
functionality of /dev/zero ?
/dev/zero is a Linux special device. It can be
considered a source of zeroes. You cannot send something to /dev/zero,
but you can read zeroes from it.
4. Now issue the following command:
dd if=/dev/random of=random.txt count=1 bs=100 ; od random.txt
dd will copy one times (count=1) a block of size 100 bytes (bs=100)
from the file /dev/random to \~/test/random.txt. Can you describe the
functionality of /dev/random ?
/dev/random acts as a
random number generator on your Linux machine.
5. Issue the following two commands, and look at the first character of each output line.
ls -l /dev/sd* /dev/hd*
ls -l /dev/tty* /dev/input/mou*
The first ls will show block(b) devices, the second ls shows character(c) devices. Can you tell the difference between block and character devices ?
Block devices are always written to (or read from) in blocks. For hard disks, blocks of 512 bytes are common. Character devices act as a stream of characters (or bytes). Mouse and keyboard are typical character devices.
6. Use cat to display /etc/hosts and /etc/resolv.conf. What is your
idea about the purpose of these files ?
/etc/hosts/etc/hosts contains hostnames with their ip address
/etc/resolv.conf/etc/resolv.conf should contain the ip address of a DNS name server.
7. Are there any files in /etc/skel/ ? Check also for hidden files.
Issue "ls -al /etc/skel/". Yes, there should be hidden files there.
8. Display /proc/cpuinfo. On what architecture is your Linux running
?
The file should contain at least one line with Intel or other cpu.
9. Display /proc/interrupts. What is the size of this file ? Where is
this file stored ?
The size is zero, yet the file contains data. It is not stored anywhere because /proc is a virtual file system that allows you to talk with the kernel. (If you answered \"stored in RAM-memory, that is also correct...).
10. Can you enter the /root directory ? Are there (hidden) files ?
Try "cd /root". The /root directory is not accessible for normal users on most modern Linux systems.
11. Are ifconfig, fdisk, parted, shutdown and grub-install present in
/sbin ? Why are these binaries in /sbin and not in /bin ?
Because those files are only meant for system administrators.
12. Is /var/log a file or a directory ? What about /var/spool ?
Both are directories.
13. Open two command prompts (Ctrl-Shift-T in gnome-terminal) or
terminals (Ctrl-Alt-F1, Ctrl-Alt-F2, ...) and issue the who am i in
both. Then try to echo a word from one terminal to the other.
tty-terminal: echo Hello > /dev/tty1
pts-terminal: echo Hello > /dev/pts/1
14. Read the man page of random and explain the difference between
/dev/random and /dev/urandom.
man 4 random