Chapter 10. System tips

Table of Contents

10.1. The screen program
10.1.1. The use scenario for the screen command
10.1.2. Key bindings for the screen command
10.1.3. A screen-like program for X window system
10.2. Data recording and presentation
10.2.1. The log daemon
10.2.2. Log analyzer
10.2.3. Recording the shell activities cleanly
10.2.4. Customized display of text data
10.2.5. Colorized shell echo
10.2.6. Colorized commands
10.2.7. Recording the graphic image of an X application
10.2.8. Recording changes in configuration files
10.3. Data storage tips
10.3.1. Partition configuration
10.3.2. Accessing partition using UUID
10.3.3. Filesystem configuration
10.3.4. Filesystem creation and integrity check
10.3.5. Optimization of filesystem by mount options
10.3.6. Optimization of filesystem via superblock
10.3.7. Optimization of harddisk
10.3.8. Expand usable storage space via LVM
10.3.9. Expand usable storage space by mounting another partition
10.3.10. Expand usable storage space using symlink
10.3.11. Expand usable storage space using aufs
10.4. Data encryption tips
10.4.1. Removable disk encryption with dm-crypt/LUKS
10.4.2. Encrypted swap partition with dm-crypt
10.4.3. Automatically encrypting files with eCryptfs
10.4.4. Automatically mounting eCryptfs
10.5. Monitoring, controlling, and starting program activities
10.5.1. Time a process
10.5.2. The scheduling priority
10.5.3. The ps command
10.5.4. The top command
10.5.5. List files opened by a process
10.5.6. Trace program activities
10.5.7. Identify processes using files or sockets
10.5.8. Repeating a command with a constant interval
10.5.9. Repeating a command looping over files
10.5.10. Starting a program from GUI
10.5.11. Customizing program to be started
10.5.12. Kill a process
10.5.13. Schedule tasks once
10.5.14. Schedule tasks regularly
10.5.15. Alt-SysRq
10.6. System maintenance tips
10.6.1. Who is logged on
10.6.2. Warn everyone
10.6.3. The hardware identification
10.6.4. The hardware configuration
10.6.5. System and hardware time
10.6.6. The terminal configuration
10.6.7. The sound infrastructure
10.6.8. Disable the screen saver
10.6.9. Disable the sound (beep)
10.6.10. Memory usage
10.6.11. System security and integrity check
10.7. The kernel
10.7.1. Linux kernel 2.6
10.7.2. Kernel headers
10.7.3. Kernel and module compile
10.7.4. Kernel source compile: Debian standard method
10.7.5. Module source compile: Debian standard method
10.7.6. Kernel source compile: classic method
10.7.7. Non-free hardware drivers
10.8. The chroot
10.8.1. Run a different Debian distribution with chroot
10.8.2. Setting up login for chroot
10.8.3. Setting up X for chroot
10.8.4. Run other distributions with chroot
10.8.5. Build packages under chroot
10.8.6. Other virtualization tools

Here, I will describe basic tips to configure and manage systems, mostly from the console.

10.1. The screen program

The screen program is a very useful tool for people to access remote sites via unreliable or intermittent connections since it support interrupted network connections.

Table 10.1.  List of programs to support interrupted network connections.

package

popcon

size

description

screen

V:10, I:29

1036

terminal multiplexer with VT100/ANSI terminal emulation

xmove

V:0.05, I:0.5

372

allows you to move programs between X Window System displays


10.1.1. The use scenario for the screen command

The screen(1) program not only allows one terminal window to work with multiple processes, but also allows remote shell process to survive interrupted connections. Here is a typical use scenario of the screen(1) program.

  1. You login to a remote machine.

  2. You start the screen command on a single console.

  3. You execute multiple programs in screen windows created with ^A c ("Control-A" followed by "c").

  4. You switch among the multiple screen windows by ^A n ("Control-A" followed by "n").

  5. Suddenly you need to leave your terminal, but you don't want to lose your active work by keeping the connection.

  6. You detach the screen session by any methods such as:

    • brutally unplugging your network connection,

    • typing ^A d ("Control-A" followed by "d") and manually logging out from the remote connection, or

    • typing ^A DD ("Control-A" followed by "DD") to have screen detach and log you out.

  7. You log in again to the same remote machine (even from a different terminal).

  8. You enter the "screen -r" command.

  9. The screen program will magically reattach all previous screen windows with all actively running programs.

[Tip] Tip

You can save connection fees for metered network connections such as dial-up and packet ones, because you can leave a process active while disconnected, and then re-attach it later when you connect again.

10.1.2. Key bindings for the screen command

In screen session, all keyboard inputs are sent to your current window except for the command keystroke, by default ^A ("Control-A"). All screen commands are entered by typing ^A plus a single key [plus any parameters]. Here are important ones to remember:

Table 10.2.  List of key bindings for screen.

key binding

meaning

^A ?

show a help screen (display key bindings)

^A c

create a new window and switch to it

^A n

go to next window

^A p

go to previous window

^A 0

go to window number 0

^A 1

go to window number 1

^A w

show a list of windows

^A a

send a Ctrl-A to current window as keyboard input

^A h

write a hardcopy of current window to file

^A H

begin/end logging current window to file

^A ^X

lock the terminal (password protected)

^A d

detach screen session from the terminal

^A DD

detach screen session and log out


See screen(1) for details.

10.1.3. A screen-like program for X window system

The xmove package enables support for mobile X clients; that is, X clients can move between displays. See xmove(1).

10.2. Data recording and presentation

10.2.1. The log daemon

Many programs record their activities under the /var/log/ directory.

  • The kernel log daemon: klogd(8)

  • The system log daemon: syslogd(8)

See Section 4.5.8, “The system message” and Section 4.5.9, “The kernel message”.

10.2.2. Log analyzer

Here are notable log analyzers ("~Gsecurity::log-analyzer" in aptitude).

Table 10.3.  List of system log analyzers.

package

popcon

size

description

logwatch

V:2, I:2

2312

log analyser with nice output written in Perl

fail2ban

V:2, I:2

616

bans IPs that cause multiple authentication errors

analog

V:1.2, I:17

4608

web server log analyzer

awstats

V:1.5, I:3

4896

powerful and featureful web server log analyzer

sarg

V:1.5, I:1.5

1448

squid analysis report generator

pflogsumm

V:0.3, I:0.7

164

Postfix log entry summarizer

syslog-summary

V:0.2, I:1.0

80

summarize the contents of a syslog log file

lire

V:0.18, I:0.2

5056

full-featured log analyzer and report generator

fwlogwatch

V:0.14, I:0.2

432

Firewall log analyzer

squidview

V:0.09, I:0.6

260

monitors and analyses squid access.log files

visitors

V:0.08, I:0.3

224

fast web server log analyzer

swatch

V:0.06, I:0.2

112

Log file viewer with regexp matching, highlighting, & hooks

crm114

V:0.08, I:0.2

1120

The Controllable Regex Mutilator and Spam Filter (CRM114)

icmpinfo

V:0.07, I:0.4

84

Interpret ICMP messages


[Note] Note

CRM114 provides language infrastructure to write fuzzy filters with the TRE regex library. Its popular use is spam mail filter but it can be used as log analyzer.

10.2.3. Recording the shell activities cleanly

The simple use of the script(1) command (see: Section 2.4.9, “Recording the shell activities”) to record shell activity produces a file with control characters. This can be avoided by using the col(1) command:

$ script
Script started, file is typescript
  • do whatever ...

  • Press Ctrl-D to exit script

$ col -bx <typescript >cleanedfile
$ vim cleanedfile

If you don't have the script command (for example, during the boot process in the initramfs), you can use following instead:

$ sh -i 2>&1 | tee typescript
[Tip] Tip

Some x-terminal-emulator such as gnome-terminal can record. You may wish to extend line buffer for scrollback.

[Tip] Tip

You may use screen command with "^A H" (see Section 10.1.2, “Key bindings for the screen command”) to perform recording of console.

[Tip] Tip

You may use emacs with "M-x shell", "M-x eshell", or "M-x term" to perform recording of console. You may later use "C-x C-w" to write the buffer to a file.

10.2.4. Customized display of text data

Although pager tools such as more(1) and less(1) (see Section 2.4.5, “The pager”) and custom tools for highlighting and formatting Section 12.1.7, “Highlighting and formatting plain text data” can display text data nicely, general purpose editors (see Section 2.4.6, “The text editor”) are most versatile and customizable.

[Tip] Tip

For vim(1) and its pager mode alias view(1), ":set hls" will enable highlighted search.

10.2.5. Colorized shell echo

Shell echo to most modern terminals can be colorized using ANSI escape code (see /usr/share/doc/xterm/ctlseqs.txt.gz). E.g.:

$ RED=$(printf "\x1b[31m")
$ NORMAL=$(printf "\x1b[0m")
$ REVERSE=$(printf "\x1b[7m")
$ echo "${RED}RED-TEXT${NORMAL} ${REVERSE}REVERSE-TEXT${NORMAL}"

10.2.6. Colorized commands

Colorized commands are handy for inspecting their output in the interactive environment. I include following in my ~/.bashrc.

if [ "$TERM" != "dumb" ]; then
    eval "`dircolors -b`"
    alias ls='ls --color=always'
    alias ll='ls --color=always -l'
    alias la='ls --color=always -A'
    alias less='less -R'
    alias ls='ls --color=always'
    alias grep='grep --color=always'
    alias egrep='egrep --color=always'
    alias fgrep='fgrep --color=always'
    alias zgrep='zgrep --color=always'
else
    alias ll='ls -l'
    alias la='ls -A'
fi

The use of alias limits color effects to the interactive command usage. It has advantage over exporting environment variable "export GREP_OPTIONS='--color=auto'" since color can be seen under pager programs such as "less".

[Tip] Tip

You can turn off these colorizing aliases in the interactive environment by invoking shell with "TERM=dumb bash".

10.2.7. Recording the graphic image of an X application

There are few ways to record the graphic image of an X application, including an xterm display.

Table 10.4.  List of graphic image manipulation tools.

package

popcon

size

command

xbase-clients

V:25, I:64

84

xwd(1)

gimp

V:13, I:55

11928

GUI menu

imagemagick

V:13, I:31

4464

import(1)

scrot

V:0.2, I:1.1

76

scrot(1)


10.2.8. Recording changes in configuration files

There are specialized tools to record changes in configuration files with help of DVCS system.

Table 10.5.  List of packages to record configuration history in VCS.

package

popcon

size

description

etckeeper

V:0.2, I:0.5

296

store configuration files and its metadata with Git (default), Mercurial, or Bazaar. (new)

changetrack

V:0.07, I:0.09

152

store configuration files with RCS. (old)


I recommend to use the etckeeper package with git(1) which put entire "/etc" under VCS control. Its installation guide and tutorial are found in "/usr/share/doc/etckeeper/README.gz".

Essentially, running "sudo etckeeper init" initializes the git repository for "/etc" just like the process explained in Section 11.5.4.4, “Git for recording configuration history”) but with special hook scripts for more thorough setups.

As you change your configuration, you can use git(1) normally to record them. It will automatically record changes nicely every time you run package management commands, too.

You can browse history of "/etc" and package upgrade by executing "cd /etc; sudo gitk".

10.3. Data storage tips

Booting your system with Linux live CDs or debian-installer CDs in rescue mode make it easy for you to reconfigure data storage on your boot device. See also Section 11.2, “The binary data”.

10.3.1. Partition configuration

For partition configuration, although fdisk(8) has been considered standard, parted(8) deserves some attention. "Disk partitioning data", "partition table", "partition map", and "disk label" are all synonyms.

Most PCs use the classic Master Boot Record (MBR) scheme to hold disk partitioning data in the first sector, i.e., LBA sector 0 (512 bytes).

[Note] Note

Some new PCs with Extensible Firmware Interface (EFI), including Intel-based Macs, use GUID Partition Table (GPT) scheme to hold disk partitioning data not in the first sector.

Although fdisk(8) has been standard for the disk partitioning tool, parted(8) is replacing it.

Table 10.6.  List of disk partition management packages

package

pocon

size

description

GUID Partition Table

util-linux

V:85, I:99

1744

Miscellaneous system utilities including fdisk(8) and cfdisk(8)

Not supported

parted

V:1.1, I:8

180

The GNU Parted disk partition resizing program

Supported

gparted

V:4, I:46

1940

GNOME partition editor based on libparted

Supported

qtparted

V:0.14, I:1.1

764

KDE partition editor based on libparted

Supported

gptsync

V:0.00, I:0.11

72

Synchronize classic MBR partition table with the GPT one

Supported


[Caution] Caution

Although parted(8) claims to create and to resize filesystem too, it is safer to do such things using best maintained specialized tools such as mkfs(8) (mkfs.msdos(8), mkfs.ext2(8), mkfs.ext3(8), ...) and resize2fs(8).

[Note] Note

In order to switch between GPT and MBR, you need to erase first few blocks of disk contents directly (see Section 11.2.10, “Clear file contents”) and use "parted /dev/sdx mklabel gpt" or "parted /dev/sdx mklabel msdos" to set it. Please note "msdos" is use here for MBR.

10.3.2. Accessing partition using UUID

Although reconfiguration of your partition may yield different names for partitions, you can access them consistently. This is also helpful if you have multiple disks and your BIOS doesn't give them consistent device names.

[Tip] Tip

You can probe UUID of a block special device with the vol_id(8) command.

10.3.3. Filesystem configuration

For ext3 filesystem, the e2fsprogs package provides:

  • mkfs.ext3(8) to create new ext3 filesystem,

  • fsck.ext3(8) to check and to repair existing ext3 filesystem, and

  • tune2fs(8) to configure superblock of ext3 filesystem.

The mkfs(8) and fsck(8) commans are provided by the e2fsprogs package as front-ends to various filesystem dependent programs (mkfs.fstype and fsck.fstype). For ext3 filesystem, they are mkfs.ext3(8) and fsck.ext3(8) (they are hardlinked to mke2fs(8) and e2fsck(8)).

Similar commands are available for each filesystem supported by Linux.

Table 10.7.  List of filesystem management packages

package

popcon

size

description

e2fsprogs

V:61, I:99

2088

Utilities for the ext2/ext3/ext4 filesystems.

reiserfsprogs

V:3, I:10

1156

Utilities for the Reiserfs filesystem.

dosfstools

V:3, I:24

224

Utilities for the FAT filesystem. (Microsoft: MS-DOS, Windows)

xfsprogs

V:2, I:9

3132

Utilities for the XFS filesystem. (SGI: IRIX)

ntfsprogs

V:1.3, I:6

632

Utilities for the NTFS filesystem. (Microsoft: Windows NT, ...)

jfsutils

V:0.6, I:2

1116

Utilities for the JFS filesystem. (IBM: AIX, OS/2)

reiser4progs

V:0.08, I:0.7

1248

Utilities for the Reiser4 filesystem.

hfsprogs

V:0.03, I:0.4

324

Utilities for HFS and HFS+ filesystem. (Apple: Mac OS)

btrfs-tools

V:0.01, I:0.05

576

Utilities for the btrfs filesystem.


[Tip] Tip

Ext3 filesystem is the default filesystem for the Linux system and strongly recommended to use it unless you have some specific reasons not to. After Linux kernel 2.6.28 (Debian squeeze), ext4 filesystem will be available and expected to be the default filesystem for the Linux system. btrfs filesystem is expected to be the next default filesystem after ext4 filesystem for the Linux system.

[Tip] Tip

Some tools allow access to filesystem without Linux kernel support (see Section 11.2.5, “Manipulating files without mounting disk”).

10.3.4. Filesystem creation and integrity check

The mkfs(8) command creates the filesystem on a Linux system. The fsck(8) command provides the filesystem integrity check and repair on a Linux system.

[Tip] Tip

Check files in /var/log/fsck/ for the result of the fsck(8) command run from the boot script.

[Caution] Caution

It is generally not safe to run fsck on mounted filesystems.

[Tip] Tip

Use "shutdown -F -r now" to force to run the fsck(8) command safely on all filesystems including root file system on reboot. See the shutdown(8) manpage for more.

10.3.5. Optimization of filesystem by mount options

Performance and characteristics of a filesystem can be optimized by mount options used on it (see fstab(5) and mount(8)). For example:

  • "defaults" option implies default options: "rw,suid,dev,exec,auto,nouser,async". (general)

  • "noatime" or "relatime" option is very effective for speeding up the read access. (general)

  • "user" option allows an ordinary user to mount the file system. This option implies "noexec,nosuid,nodev" option combination. (general, used for CD and floppy)

  • "noexec,nodev,nosuid" option combination is used to enhance security. (general)

  • "noauto" option limits mounting by explicit operation only. (general)

  • "data=journal" option for ext3fs can enhance data integrity against power failure with some loss of write speed.

[Tip] Tip

You need to provide kernel boot parameter "rootflags=data=journal" to deploy "data=journal" option for the root file system formatted with ext3fs.

10.3.6. Optimization of filesystem via superblock

Characteristics of a filesystem can be optimized via its superblock using the tune2fs(8) command. For example on /dev/hda1:

  • Execution of "sudo tune2fs -l /dev/hda1" will display the contents of its filesystem superblock.

  • Execution of "sudo tune2fs -c 50 /dev/hda1" will change frequency of filesystem checks (fsck execution during boot-up) to every 50 boots.

  • Execution of "sudo tune2fs -j /dev/hda1" will add journaling capability to the filesystem, i.e. filesystem conversion from ext2 to ext3. (Do this on the unmounted filesystem.)

  • Execution of "sudo tune2fs -O extents,uninit_bg,dir_index /dev/hda1 && fsck -pf /dev/hda1" will convert it from ext3 to ext4. (Do this on the unmounted filesystem.)

[Warning] Warning

Filesystem conversion for the boot device to the ext4 filesystem should be avoided until GRUB boot loader supports the ext4 filesystem well and installed Linux Kernel version is newer than 2.6.28.

[Tip] Tip

Despite its name, tune2fs(8) works not only on the ext2 filesystem but also on the ext3 and ext4 filesystems.

10.3.7. Optimization of harddisk

[Warning] Warning

Please check your hardware and read manpage of hdparam(8) before playing with harddisk configuration because this may be quite dangerous for the data integrity.

You can test disk access speed of a harddisk, e.g. /dev/hda, by "hdparm -tT /dev/hda". For some harddisk connected with (E)IDE, you can speed it up with "hdparm -q -c3 -d1 -u1 -m16 /dev/hda" by enabling the "(E)IDE 32-bit I/O support", enabling the "using_dma flag", setting "interrupt-unmask flag", and setting the "multiple 16 sector I/O" (dangerous!).

You can test write cache feature of a harddisk, e.g. /dev/sda, by "hdparm -W /dev/sda". You can disable its write cache feature with "hdparm -W 0 /dev/sda".

You may be able to read badly pressed CDROMs on modern high head CD-ROM drive by slowing it down with "setcd -x 2.

10.3.8. Expand usable storage space via LVM

For partitions created on Logical Volume Manager (Linux) at install time, they can be resized easily by concatenating extents onto them or truncating extents from them over multiple storage devices without major system reconfiguration.

[Caution] Caution

Deployment of the current LVM system may degrade guarantee against filesystem corruption offered by journaled file systems such as ext3fs unless their system performance is sacrificed by disabling write cache of harddisk.

10.3.9. Expand usable storage space by mounting another partition

If you have an empty partition (e.g., /dev/sdx), you can format it with mkfs.ext3(1) and mount(8) it to a directory where you need more space. (You need to copy original data contents.)

$ sudo mv work-dir old-dir
$ sudo mkfs.ext3 /dev/sdx
$ sudo mount -t ext3 /dev/sdx work-dir
$ sudo cp -a old-dir/* work-dir
$ sudo rm -rf old-dir

10.3.10. Expand usable storage space using symlink

If you have an empty directory (e.g., /path/to/emp-dir) in another partition with usable space, you can create a symlink to the directory with ln(8).

$ sudo mv work-dir old-dir
$ sudo mkdir -p /path/to/emp-dir
$ sudo ln -sf /path/to/emp-dir work-dir
$ sudo cp -a old-dir/* work-dir
$ sudo rm -rf old-dir
[Caution] Caution

Some software may not function well with "symlink to a directory".

10.3.11. Expand usable storage space using aufs

If you have usable space in another partition (e.g., /path/to/), you can create a directory in it and stack that on to a directory where you need space with aufs.

$ sudo mv work-dir old-dir
$ sudo mkdir -p /path/to/emp-dir
$ sudo mount -t aufs -o br:/path/to/emp-dir:old-dir none work-dir
[Caution] Caution

Use of aufs for long term data storage is not good idea since it is under development and its design change may introduce issues.

[Tip] Tip

In order to use aufs, its utility package aufs-tools and kernel module package for aufs such as aufs-modules-2.6-amd64 need to be installed.

[Note] Note

aufs is used to provide writable root filesystem by many modern live CD projects.

10.4. Data encryption tips

Since gaining root privilege is relatively easy with physical access (see Section 5.7.4, “Securing the root password”), it can not secure your private and sensitive data against possible theft of your PC. You must deploy data encryption technology to do it. Although GNU privacy guard (see Section 11.3, “Data security infrastructure”) can encrypt files, it takes some user efforts.

dm-crypt and eCryptfs facilitates automatic data encryption natively via Linux kernel modules with minimal user efforts.

Table 10.8.  List of data encryption utilities.

package

popcon

size

function

cryptsetup

V:2, I:4

840

Utilities for encrypted block device (dm-crypt / LUKS)

cryptmount

V:0.11, I:0.5

292

Utilities forencrypted block device (dm-crypt / LUKS) with focus on mount/unmount by normal users

ecryptfs-utils

V:0.03, I:0.17

396

Utilities for encrypted stacked filesystem (eCryptfs)


Dm-crypt is a cryptographic filesystem using device-mapper. Device-mapper maps one block device to another.

eCryptfs is another cryptographic filesystem using stacked filesystem. Stacked filesystem stacks itself on top of an existing directory of a mounted filesystem.

[Note] Note

Entire Debian system can be installed on a encrypted disk by the debian installer (lenny or newer) using dm-crypt/LUKS and initramfs.

[Caution] Caution

Data encryption costs CPU time etc. Please weigh its benefits and costs.

[Tip] Tip

See Section 11.3, “Data security infrastructure” for user space encryption utility: GNU Privacy Guard.

10.4.1. Removable disk encryption with dm-crypt/LUKS

You can encrypt contents of removable mass storage devices, e.g. USB memory stick on /dev/sdx, using dm-crypt/LUKS. You simply formatting it as:

# badblocks -c 10240 -s -w -t random -v /dev/sdx
# shred -v -n 1 /dev/sdx
# fdisk /dev/sdx
... "n" "p" "1" "return" "return" "w"
# cryptsetup luksFormat /dev/sdx1
...
# cryptsetup luksOpen /dev/sdx1 sdx1
...
# ls -l /dev/mapper/
total 0
crw-rw---- 1 root root  10, 60 2008-10-04 18:44 control
brw-rw---- 1 root disk 254,  0 2008-10-04 23:55 sdx1
# mkfs.vfat /dev/mapper/sdx1
...
# cryptsetup luksClose sdx1

Then, it can be mounted just like normal one on to /media/<disk_label>, except for asking password (see Section 11.1.10, “Removable mass storage device”) under modern desktop environment, such as Gnome using gnome-mount(1). The difference is that every data written to it is encrypted. You may alternatively format media in different file format, e.g., ext3 with "mkfs.ext3 /dev/sdx1".

[Note] Note

If you are really paranoid for the security of data, you may need to overwrite multiple times in the above example. This operation is very time consuming though.

10.4.2. Encrypted swap partition with dm-crypt

If your original /etc/fstab contains:

/dev/sda7 swap sw 0 0

then you can enable encrypted swap partition using dm-crypt as

# swapoff -a
# echo "cswap /dev/sda7 /dev/urandom swap" >> /etc/crypttab
# perl -i -p -e "s/\/dev\/sda7/\/dev\/mapper\/cswap/" /etc/fstab
# swapon -a

10.4.3. Automatically encrypting files with eCryptfs

You can encrypt files written under "~/Private/" automatically using eCryptfs and the ecryptfs-utils package.

  • run "ecryptfs-setup-private" and set up "~/Private/" by following prompts.

  • activate "~/Private/" by issuing "ecryptfs-mount-private".

  • move sensitive data files to "~/Private/" and make symlinks.

  • move sensitive data directories to "~/Private/" and make symlinks.

  • do the same for "~/.gnupg" and other directories containing sensitive data.

  • create symlink from "~/.ssh" to "~/Private/.ssh"

  • deactivate "~/Private/" by issuing "ecryptfs-umount-private".

  • activate "~/Private/" by issuing "ecryptfs-mount-private" as you need encrypted data.

[Tip] Tip

Files and directories with "go-r" permission such as "~/.cvspass", "~/.fetchmailrc", "~/.ssh/identity", "~/.ssh/id_rsa", "~/.ssh/id_dsa", "~/.gnupg/", "~/.gnome2/", ... can be considered sensitive data.

[Tip] Tip

Since eCryptfs selectively encrypt only the sensitive files, its system cost is much less than using dm-crypt on the entire root or home device. It does not require any special on-disk storage allocation effort but cannot keep all filesystem metadata confidential.

10.4.4. Automatically mounting eCryptfs

If you use your login password for wrapping encryption keys, you can automate mounting eCryptfs via Pluggable Authentication Module by having active lines in /etc/pam.d/common-auth as:

auth required pam_unix.so nullok_secure
auth required pam_ecryptfs.so unwrap

and active lines in /etc/pam.d/common-session as:

session required pam_unix.so
session optional pam_ecryptfs.so unwrap

This is quite convienient.

[Caution] Caution

If you use your login password for wrapping encryption keys, your encrypted data are as secure as your user login password (see Section 5.3, “Good password”). Unless you are careful to set up a strong password, your data will be at risk when someone runs password cracking software after stealing your laptop (see Section 5.7.4, “Securing the root password”). The squeeze version of the ecryptfs-utils package comes with option to have independent password for wrapping and to set up user's entire home directory for encryption. This is an actively developed package.

10.5. Monitoring, controlling, and starting program activities

Program activities can be monitored and controlled using specialized tools.

Table 10.9.  List of tools for monitoring and controlling program activities

package

popcon

size

description

time

V:6, I:86

152

The time(1) command runs a program to report system resource usages with respect to time.

coreutils

V:87, I:99

11448

The nice(1) command runs a program with modified scheduling priority.

bsdutils

V:61, I:99

168

The renice(1) command modifies the scheduling priority of a running process.

powertop

V:0.5, I:7

424

On Intel-based laptops powertop(1) gives information about system power use.

procps

V:82, I:99

748

The /proc file system utilities: ps(1), top(1), kill(1), watch(1), ...

psmisc

V:51, I:89

508

The /proc file system utilities: killall(1), fuser(1), pstree(1)

cron

V:86, I:99

320

This package run processes according to a schedule (in background).

at

V:51, I:84

220

The at(1) or batch(1) commands run a job at a specified time or below certain load level.

lsof

V:16, I:92

424

The lsof(8) command lists open files by a running process using "-p" option.

strace

V:9, I:88

420

The strace(1) command traces system calls and signals.

ltrace

V:0.3, I:2

220

The ltrace(1) command traces library calls.

xtrace

V:0.02, I:0.15

216

The xtrace(1) command traces communication between X11 client and server.


10.5.1. Time a process

Display time used by the process invoked by the command.

# time some_command >/dev/null
real    0m0.035s       # time on wall clock (elapsed real time)
user    0m0.000s       # time in user mode
sys     0m0.020s       # time in kernel mode

10.5.2. The scheduling priority

A nice value is used to control the scheduling priority for the process.

Table 10.10.  List of nice values for the scheduling priority.

nice value

scheduling priority

19

lowest priority process (nice)

0

very high priority process for user.

-20

very high priority process for root. (not-nice)


# nice  -19 top                                      # very nice
# nice --20 wodim -v -eject speed=2 dev=0,0 disk.img # very fast

Sometimes an extreme nice value does more harm than good to the system. Use this command carefully.

10.5.3. The ps command

The ps(1) command on the Debian support both BSD and SystemV features and helps to identify the process activity statically.

Table 10.11.  List of ps command styles.

style

typical command

feature

BSD

ps aux

display %CPU %MEM

System V

ps -efH

display PPID


For the zombie (defunct) children process, you can kill them by the parent process ID identified in the (PPID) field.

The pstree(1) command display a tree of processes.

10.5.4. The top command

The top(1) command on the Debian has rich features and helps to identify what process is acting funny dynamically.

Table 10.12.  List of commands for top.

command key

response

h or ?

To show help.

f

To set/reset display field.

o

To reorder display field.

F

To set sort key field.

k

To kill a process.

r

To renice a process.

q

To quit the top command.


10.5.5. List files opened by a process

You can list all files opened by a process with a process ID (PID), e.g. 1 as:

$ sudo lsof -p 1

PID=1 is usually init program.

10.5.6. Trace program activities

You can trace program activity with strace(1), ltrace(1), or xtrace(1) commands for system calls and signals, library calls, or communication between X11 client and server. For example:

$ sudo strace ls
...

10.5.7. Identify processes using files or sockets

You can also identify processes using files or sockets by fuser(1). For example:

$ sudo fuser -v /var/log/mail.log
                     USER        PID ACCESS COMMAND
/var/log/mail.log:   root       2946 F.... syslogd

You see that file /var/log/mail.log is open for writing by the syslogd(8) command.

$ sudo fuser -v smtp/tcp
                     USER        PID ACCESS COMMAND
smtp/tcp:            Debian-exim   3379 F.... exim4

Now you know your system runs exim4(8) to handle TCP connections to SMTP port (25).

10.5.8. Repeating a command with a constant interval

The watch(1) command executes a program repeatedly with a constant interval while showing its output in fullscreen.

$ watch w

This will display who is logged on to the system updated every 2 seconds.

10.5.9. Repeating a command looping over files

There are several ways to repeat a command looping over files matching some condition, e.g. matching glob pattern "*.ext".

  • Shell for-loop method (see Section 13.1.4, “Shell loops”):
    for x in *.ext; do if [ -f "$x"]; then command "$x" ; fi; done
    
  • find(1) and xargs(1) combination:

    find . -type f -maxdepth 1 -name '*.ext' -print0 | xargs -0 -n 1 command
    
  • find(1) with "-exec" option with a command:

    find . -type f -maxdepth 1 -name '*.ext' -exec command '{}' \;
    
  • find(1) with "-exec" option with a short shell script:

    find . -type f -maxdepth 1 -name '*.ext' -exec sh -c "command '{}' && echo 'successful'" \;
    

The above examples are written to ensure proper handling of funny file names such as ones containing spaces. See Section 11.1.5, “Idioms for the selection of files” for more advance uses of find(1).

10.5.10. Starting a program from GUI

You can set up to start a process from graphical user interface (GUI).

Under Gnome desktop environment, a program program can be started with proper argument by drag-and-drop of an icon to the launcher icon or by "Open with ..." menu with right clicking. KDE can do the equivalent, too. Here is an example for Gnome to set up mc program started in gnome-terminal:

  • create an executable program "mc-term" as:

# cat >/usr/local/mc-term <<EOF
#!/bin/sh
gnome-terminal -e "mc $1"
EOF
# chmod 755 /usr/local/mc-term
  • create a desktop launcher
    • right clicking desktop space to select "Create Launcher ..."

      • set "Type" to "Application"

      • set "Name" to "mc"

      • set "Command" to "mc-term %f"

      • click "OK"

  • create an open-with association
    • right click folder to select "Open with Other Application ..."

      • click open "Use a custom command" dialog and enter "mc-term %f"

      • click "Open".

[Tip] Tip

Launcher is a file at "~/Desktop" with "desktop" as its extension.

10.5.11. Customizing program to be started

Some programs start another program automatically. Here are check points for customizing this process:

  • configuration file of the parent program such as "/etc/mc/mc.ext".

  • system configuration menu such as "System" -> "Preferences" -> "Preferred Application" for Gnome.

  • environment variables such as "BROWSER", "EDITOR", "VISUAL", and "PAGER" (see eviron(7)).

  • the update-alternatives(8) system for programs such as "editor", "view", "x-www-browser", "gnome-www-browser", and "www-browser" (see Section 2.4.7, “Setting a default text editor”).

  • the "$HOME/.mailcap" and "/etc/mailcap" file contents which associate MIME type with program (see mailcap(5)).

  • the the "$HOME/.mime.types" and "/etc/mime.types" file contents which associate file name extension with MIME type (see run-mailcap(1)).

[Tip] Tip

The update-mime(8) command updates the "/etc/mailcap" file using "/etc/mailcap.order" file (see mailcap.order(5)).

[Tip] Tip

The debianutils package provides sensible-browser(1), sensible-editor(1), and sensible-pager(1) commands which make sensible decisions on which editor, pager, and web browser to call, respectively. I recommend you to read these shell commands.

10.5.12. Kill a process

Use the kill(1) command to kill (or send a signal to) a process by the process ID.

Use killall(1) or pkill(1) commands to do the same by the process command name and other attributes.

Table 10.13.  List of frequently used signals for kill command.

signal value

signal name

function

1

HUP

restart daemon

15

TERM

normal kill

9

KILL

kill hard


10.5.13. Schedule tasks once

Run the at(1) command to schedule a one-time job:

$ echo 'command -args'| at 3:40 monday

10.5.14. Schedule tasks regularly

Use cron(8) to schedule tasks regularly. See crontab(1) and crontab(5).

Run the command "crontab -e" to create or edit a crontab file to set up regularly scheduled events.

Example of a crontab file:

# use /bin/sh to run commands, no matter what /etc/passwd says
SHELL=/bin/sh
# mail any output to paul, no matter whose crontab this is
MAILTO=paul
# Min Hour DayOfMonth Month DayOfWeek command (Day... are OR'ed)
# run at 00:05, every day
5  0  *  * *   $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
# run at 14:15 on the first of every month -- output mailed to paul
15 14 1  * *   $HOME/bin/monthly
# run at 22:00 on weekdays(1-5), annoy Joe. % for newline, last % for cc:
0 22 *   * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%.%%
23 */2 1 2 *   echo "run 23 minutes after 0am, 2am, 4am ..., on Feb 1"
5  4 *   * sun echo "run at 04:05 every sunday"
# run at 03:40 on the first Monday of each month
40 3 1-7 * *   [ "$(date +%a)" == "Mon" ] && command -args
[Tip] Tip

For the system not running continuously, install the anacron package to schedule periodic command at the specified intervals as closely as machine-uptime permits.

10.5.15. Alt-SysRq

Insurance against system malfunction is provided by the kernel compile option "Magic SysRq key" (SAK key) which is now the default for the Debian kernel. Pressing Alt-SysRq followed by one of the following keys does the magic of rescuing control of the system:

Table 10.14.  List of SAK command keys.

key following Alt-SysRq

function

r

Unraw restores the keyboard after things like X crashes.

0

Changing the console loglevel to 0 reduces error messages.

k

SAK (system attention key) kills all processes on the current virtual console.

e

Send a SIGTERM to all processes, except for init.

i

Send a SIGKILL to all processes, except for init.

s

Sync all mounted filesystems.

u

Remount all mounted filesystems read-only (umount).

b

Reboot the system without syncing or unmounting.


The combination of "Alt-SysRq s", "Alt-SysRq u", and "Alt-SysRq r" is good for getting out of really bad situations.

See /usr/share/doc/linux-doc-2.6.*/Documentation/sysrq.txt.gz .

[Caution] Caution

The Alt-SysRq feature may be considered a security risk by allowing users access to root-privileged functions. Placing "echo 0 >/proc/sys/kernel/sysrq" in /etc/rc.local or "kernel.sysrq = 0" in /etc/sysctl.conf will disable the Alt-SysRq feature.

[Tip] Tip

From SSH terminal etc., you can use the Alt-SysRq feature by writing to the /proc/sysrq-trigger. For example, "echo s > /proc/sysrq-trigger; echo u > /proc/sysrq-trigger" from the root shell prompt will sync and umount all mounted filesystems.

10.6. System maintenance tips

10.6.1. Who is logged on

You can check who is logged on to the system with w(1) or who(1) commands.

10.6.2. Warn everyone

You can send message to everyone who is logged on to the system with the wall(1) command:

$ echo "We are shutting down in 1 hour" | wall

10.6.3. The hardware identification

For the PCI-like devices (AGP, PCI-Express, CardBus, ExpressCard, etc.), lspci(8) command (probably with "-nn" option) is a good start for the hardware identification

Alternatively, you can identify the hardware by reading contents of /proc/bus/pci/devices or browsing directory tree under /sys/bus/pci (see Section 2.2.12, “procfs and sysfs”).

Table 10.15.  List of hardware identification tools.

package

popcon

size

description

pciutils

V:43, I:92

708

Linux PCI Utilities, lspci(8)

usbutils

V:27, I:97

520

Linux USB utilities, lsusb(8)

pcmciautils

V:1.0, I:16

172

PCMCIA utilities for Linux 2.6, pccardctl(8)

scsitools

V:0.2, I:1.5

484

Collection of tools for SCSI hardware management, lsscsi(8)

pnputils

V:0.02, I:0.2

108

Plug and Play BIOS utilities, lspnp(8)

procinfo

V:0.7, I:5

116

Displays system information from /proc, lsdev(8)

lshw

V:1.1, I:5

804

Information about hardware configuration, lshw(1)

discover

V:5, I:16

928

Hardware identification system, discover(8)


10.6.4. The hardware configuration

Although most of the hardware configuration on modern GUI desktop systems such as Gnome and KDE can be managed through accompanying GUI configuration tools, it is a good idea to know some basics methods to configure them.

Table 10.16.  List of hardware configuration tools.

package

popcon

size

description

hal

V:42, I:60

1980

Hardware Abstraction Layer, lshal(1)

console-tools

V:56, I:96

948

Linux console font and keytable utilities.

x11-xserver-utils

V:21, I:28

616

X server utilities. xset(1) and xmodmap(1) commands.

acpid

V:52, I:89

196

Daemon to manage events delivered by the Advanced Configuration and Power Interface (ACPI)

acpi

V:3, I:34

92

Utilities for ACPI devices

apmd

V:1.3, I:13

144

Daemon to manage events delivered by the Advanced Power Management (APM)

powersaved

V:1.0, I:1.3

1800

Daemon to manage battery, temperature, ac, cpufreq (SpeedStep, Powernow!) control and monitor with ACPI and APM supports.

noflushd

V:0.09, I:0.17

244

Allow idle hard disks to spin down

sleepd

V:0.09, I:0.12

140

Puts a laptop to sleep during inactivity

hdparm

V:10, I:34

272

Hard disk access optimization. Very effective but dangerous. You must read hdparm(8) first.

smartmontools

V:5, I:14

828

Control and monitor storage systems using S.M.A.R.T.

setserial

V:2, I:5

176

Collection of tools for serial port management.

memtest86+

V:0.5, I:4

248

Collection of tools for memory hardware management.

scsitools

V:0.2, I:1.5

484

Collection of tools for SCSI hardware management.

tpconfig

V:0.3, I:0.5

208

A program to configure touchpad devices

setcd

V:0.11, I:0.5

64

Compact disc drive access optimization.

big-cursor

I:0.2

68

Larger mouse cursors for X

lspowertweak

V:0.02, I:0.10

88

Simple front end to powertweak, lspowertweak(8)


Here, ACPI is a newer framework for the power management system than APM.

10.6.5. System and hardware time

The following will set system and hardware time to MM/DD hh:mm, CCYY.

# date MMDDhhmmCCYY
# hwclock --utc --systohc
# hwclock --show

Times are normally displayed in the local time on the Debian system but the hardware and system time usually use UTC.

If the hardware (BIOS) time is set to GMT, change the setting to UTC=yes in the /etc/default/rcS.

If you wish to update system time via network, consider to use the NTP service with the packages such as ntp, ntpdate, and chrony. See:

[Tip] Tip

The ntptrace(8) command in the ntp package can trace a chain of NTP servers back to the primary source.

10.6.6. The terminal configuration

There are several components to configure character console and ncurses(3) system features:

  • the terminfo(5) file

  • the TERM(7) environment variable

  • the setterm(1) command

  • the stty(1) command

  • the tic(1) command

  • the toe(1) command

If the terminfo entry for xterm doesn't work with a non-Debian xterm, change your terminal type from xterm to one of the feature-limited versions such as xterm-r6 when you log in to a Debian system remotely. See /usr/share/doc/libncurses5/FAQ for more. dumb is the lowest common denominator for terminfo.

10.6.7. The sound infrastructure

Device drivers for sound cards for current Linux 2.6 are provided by Advanced Linux Sound Architecture (ALSA). ALSA provides emulation mode for previous Open Sound System (OSS) for compatibility.

Run "dpkg-reconfigure linux-sound-base" to select the sound system to use ALSA via blacklisting of kernel modules. Unless you have very new sound hardware, udev infrastructure should configure your sound system.

[Tip] Tip

Use "cat /dev/urandom > /dev/audio" or the speaker-test(1) command to test speaker. (^C to stop)

[Tip] Tip

If you can not get sound, your speaker may be connected to a muted output. Modern sound system has many outputs. The alsamixer(1) command in the alsa-utils package is useful to configure volume and mute settings.

Application softwares may be configured not only to access sound devices directly but also to access them via some standardized sound server system.

Table 10.17.  List of sound packages

package

pocon

size

description

linux-sound-base

V:20, I:58

136

Base package for ALSA and OSS sound systems

alsa-base

I:58

456

ALSA driver configuration files

alsa-utils

V:38, I:58

1984

Utilities for configuring and using ALSA

oss-compat

V:17, I:25

60

OSS compatibility under ALSA preventing "/dev/dsp not found" errors

esound-common

V:27, I:67

68

Enlightened Sound Daemon (ESD) common (Enlightenment and GNOME)

esound

V:4, I:35

84

Enlightened Sound Daemon (ESD) server (Enlightenment and GNOME)

esound-clients

V:10, I:19

168

Enlightened Sound Daemon (ESD) client (Enlightenment and GNOME)

libesd-alsa0

V:2, I:2

96

Enlightened Sound Daemon (ESD) library Enlightenment and GNOME)

libesd0

V:39, I:64

92

Enlightened Sound Daemon (ESD) library (Enlightenment and GNOME) - OSS

arts

I:15

36

aRts server (KDE)

libarts1c2a

V:22, I:45

6180

aRts library (KDE)

libartsc0

V:21, I:50

72

aRts library (KDE)

jackd

V:1.5, I:6

400

JACK Audio Connection Kit. (JACK) server (low latency)

libjack0

V:14, I:26

540

JACK Audio Connection Kit. (JACK) library (low latency)

libjack0.100.0-0

I:32

48

JACK Audio Connection Kit. (JACK) library (low latency)

nas

V:0.18, I:0.3

328

Network Audio System (NAS) server

libaudio2

V:24, I:63

204

Network Audio System (NAS) library

pulseaudio

V:0.8, I:2

1264

PulseAudio server, replacement for ESD

libpulse0

V:3, I:27

508

PulseAudio client library, replacement for ESD

libpulsecore5

V:0.7, I:1.8

612

PulseAudio server library, replacement for ESD

libgstreamer0.10-0

V:18, I:61

2644

GStreamer: Gnome sound engine

libxine1

V:6, I:51

24

xine: KDE older sound engine

libphonon4

I:5

472

Phonon: KDE new sound engine


There is usually a common sound engine for each popular desktop environment. Each sound engine used by the application can choose to connect to different sound servers.

10.6.8. Disable the screen saver

For disabling the screen saver, use following commands.

Table 10.18.  List of commands for disabling the screen saver.

environment

command

The Linux console

setterm -powersave off

The X Window by turning off screensaver

xset s off

The X Window by disabling dpms

xset -dpms

The X Window by GUI configuration of screen saver

xscreensaver-command -prefs


10.6.9. Disable the sound (beep)

One can always unplug the PC speaker. Removing pcspkr kernel module does this for you.

The following will prevent the readline program used by the bash to beep when encountering "\a" (ASCII=7):

$ echo "set bell-style none">> ~/.inputrc

10.6.10. Memory usage

The kernel boot message in the /var/log/dmesg contains the total exact size of available memory.

The free(1) and top(1) commands display information on memory resources on the running system.

$ grep '^Memory' /var/log/dmesg
Memory: 990528k/1016784k available (1975k kernel code, 25868k reserved, 931k data, 296k init)
$ free -k
             total       used       free     shared    buffers     cached
Mem:        997184     976928      20256          0     129592     171932
-/+ buffers/cache:     675404     321780
Swap:      4545576          4    4545572

For my MacBook with 1GB=1048576k DRAM (video system steals some of this):

Table 10.19.  List of memory sizes reported.

report

size

Total size in dmesg

1016784k = 1GB - 31792k

Free in dmesg

990528k

Total under shell

997184k

Free under shell

20256k


Do not worry about the large size of "used" and the small size of "free" in the "Mem:" line, but read the one under them (675404 and 321780 in the example below) and relax.

10.6.11. System security and integrity check

Poor system maintenance may expose your system to external exploitation.

For system security and integrity check, you should start with:

Table 10.20.  List of tools for system security and integrity check

package

popcon

size

description

logcheck

V:3, I:4

264

This mails anomalies in the system logfiles to the administrator

debsums

V:2, I:3

236

This verifies installed package files against MD5 checksums.

chkrootkit

V:2, I:6

852

Rootkit detector.

clamav

V:2, I:10

420

Anti-virus utility for Unix - command-line interface.

tiger

V:0.8, I:1.0

3072

Report system security vulnerabilities

tripwire

V:0.5, I:0.7

5020

File and directory integrity checker

john

V:0.4, I:1.8

476

Active password cracking tool

aide

V:0.3, I:0.5

1112

Advanced Intrusion Detection Environment - static binary

bastille

V:0.2, I:0.6

1484

Security hardening tool

integrit

V:0.13, I:0.2

440

A file integrity verification program

crack

V:0.05, I:0.3

204

Password guessing program


Here is a simple script to check for typical world writable incorrect file permissions.

# find / -perm 777 -a \! -type s -a \! -type l -a \! \( -type d -a -perm 1777 \)
[Caution] Caution

Since the debsums package uses MD5 checksums stored locally, it can not be fully trusted as the system security audit tool against malicious attacks.

10.7. The kernel

Debian distributes modularized Linux kernel as packages for supported architectures.

10.7.1. Linux kernel 2.6

There are few notable features on Linux kernel 2.6 compared to 2.4.

  • Devices are created by the udev system (see Section 4.5.10, “The udev system”).

  • Read/write accesses to IDE CD/DVD devices do not use the ide-scsi module.

  • Network packet filtering functions use iptable kernel modules.

10.7.2. Kernel headers

Most normal programs don't need kernel headers and in fact may break if you use them directly for compiling. They should be compiled against the headers in /usr/include/linux and /usr/include/asm provided by the libc6-dev package (created from the glibc source package) on the Debian system.

[Note] Note

For compiling some kernel-specific programs such as the kernel modules from the external source and the automounter daemon (amd), you must include path to the corresponding kernel headers, e.g. -I/usr/src/linux-particular-version/include/ , to your command line. The module-assistant package helps users to build and install module package(s) easily for one or more custom kernels with the m-a(8) command.

10.7.3. Kernel and module compile

Debian has its own method of compiling the kernel and related modules.

Table 10.21.  List of key packages to be installed for the kernel recompilation on the Debian system

package

popcon

size

description

build-essential

I:40

48

essential packages for building Debian packages: make, gcc, ...

bzip2

V:51, I:81

132

compress and decompress utilities for bz2 files

libncurses5-dev

V:4, I:28

6812

developer's libraries and docs for ncurses

git-core

V:4, I:8

7164

git: distributed revision control system used by the Linux kernel

fakeroot

V:4, I:26

456

provide fakeroot environment for building package as non-root

initramfs-tools

V:29, I:96

412

tool to build an initramfs (Debian specific)

kernel-package

V:3, I:18

2304

tool to build Linux kernel packages (Debian specific)

module-assistant

V:3, I:22

512

tool to help build module packages (Debian specific)

devscripts

V:2, I:13

1592

helper scripts for a Debian Package maintainer (Debian specific)

linux-tree-2.6.*

I:0.15

128

Linux kernel source tree for building Debian kernel images (Debian specific)


If you use initrd in Section 4.3, “Stage 2: the boot loader”, make sure to read the related information in initramfs-tools(8), update-initramfs(8), mkinitramfs(8) and initramfs.conf(5).

[Warning] Warning

Do not put symlinks to the directories in the source tree (e.g. /usr/src/linux*) from /usr/include/linux and /usr/include/asm when compiling the Linux kernel source. (Some outdated documents suggest this.)

[Note] Note

When compiling the latest Linux kernel on the Debian stable system, the use of backported latest tools from the Debian unstable may be needed.

10.7.4. Kernel source compile: Debian standard method

The Debian standard method for compiling kernel source to create a custom kernel package uses make-kpkg(1) command. The official documentation is in (the bottom of) /usr/share/doc/kernel-package/README.gz. See kernel-pkg.conf(5) and kernel-img.conf(5) for customization.

Here is an example for amd64 system:

# aptitude install linux-tree-<version>
$ cd /usr/src
$ tar -xjvf linux-source-<version>.tar.bz2
$ cd linux-source-<version>
$ cp /boot/config-<oldversion> .config
$ make menuconfig
 ...
$ make-kpkg clean
$ fakeroot make-kpkg --append_to_version -amd64 --initrd --revision=rev.01 kernel_image modules_image
$ cd ..
# dpkg -i linux-image*.deb
  • reboot to new kernel with "shutdown -r now" .

[Caution] Caution

When you intend to create a non-modularized kernel compiled only for one machine, invoke make-kpkg command without "--initrd" option since initrd is not used. Invocation of "make oldconfig" and "make dep" are not required since "make-kpkg kernel_image" invokes them.

10.7.5. Module source compile: Debian standard method

The Debian standard method for creating and installing a custom module package for a custom kernel package uses module-assistant(8) command and module-source packages. For example, following will build the unionfs kernel module package and installs it.

$ sudo aptitude install module-assistant
...
$ sudo aptitude install unionfs-source unionfs-tools unionfs-utils
$ sudo m-a update
$ sudo m-a prepare
$ sudo m-a auto-install unionfs
...
$ sudo apt-get autoremove

10.7.6. Kernel source compile: classic method

You can still build Linux kernel from the pristine sources with the classic method. You must take care the details of the system configuration manually.

$ cd /usr/src
$ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-<version>.tar.bz2
$ tar -xjvf linux-<version>.tar.bz2
$ cd linux-<version>
$ cp /boot/config-<version> .config
$ make menuconfig
 ...
$ make dep; make bzImage
$ make modules
# cp ./arch/x86_64/boot/bzImage /boot/vmlinuz-<version>
# make modules_install
# depmod -a
# update-initramfs -c -k <version>
  • set up bootloader
    • edit /etc/lilo.conf and run /sbin/lilo, if you use lilo .

    • edit /boot/grub/menu.lst, if you use grub .

  • reboot to new kernel with "shutdown -r now" .

10.7.7. Non-free hardware drivers

Although most of hardware drivers are available as free software and as a part of the Debian system, you may need to load some non-free external drivers to support some hardwares, such as Winmodem, on your system.

Check pertinent resources:

10.8. The chroot

The chroot(8) program is most basic way to run different instances of the GNU/Linux environment on a single system simultaneously without rebooting. I will explain simple chroot systems in the following as examples.

For serious chroot setup with the detail configuration, please consider to use the specialized schroot package.

10.8.1. Run a different Debian distribution with chroot

A chroot Debian environment can easily be created by the debootstrap or cdebootstrap command.

For example, the following will create a sid chroot on /sid-root while having fast Internet access:

main # debootstrap sid /sid-root http://ftp.debian.org/debian/
  • watch it download the whole system

main # echo "proc-sid    /sid-root/proc     proc   none 0 0" >> /etc/fstab
main # echo "devpts-sid  /sid-root/dev/pts  devpts defaults 0 0" >> /etc/fstab
main # mount -a
main # cp -f /etc/passwd /sid-root/etc/passwd
main # cp -f /etc/shadow /sid-root/etc/shadow
main # cp -f /etc/group  /sid-root/etc/group
main # cp -f /etc/hosts  /sid-root/etc/hosts
main # chroot /sid-root /bin/bash
chroot # cd /dev; /sbin/MAKEDEV generic ; cd -
chroot # vi /etc/apt/sources.list
  • point the source to unstable

chroot # aptitude update
...
chroot # aptitude install locales
...
  • add "en_US.UTF-8" as locale and make it default

Do you want to continue? [Y/n/?] y
chroot # aptitude install mc vim
...
Do you want to continue? [Y/n/?] y
...
chroot # exit
main #

At this point you should have a fully working Debian sid system, where you can play around without fear of affecting your main Debian installation.

[Caution] Caution

If you use bind mount for directories such as home directory in the chroot, you must be careful for its side effects. I heard people lost their home directory after executing "rm -rf /sid-root" without unbinding their home directory in the chroot. A bind mount is not normally visible with "df", you need to execute "df -a" to see it.

This debootstrap trick can also be used to install Debian to a system without using a Debian install disk, but instead from another GNU/Linux distribution.

10.8.2. Setting up login for chroot

Typing "chroot /sid-root /bin/bash" is easy, but it retains all sorts of environment variables that you may not want, and has other issues. A much better approach is to run another login process on a separate virtual terminal where you can log in to the chroot directly.

Since on default Debian systems tty1 to tty6 run Linux consoles and tty7 runs the X Window System, let's set up tty8 for a chrooted console as an example. After creating a chroot system, type from the root shell of the main system:

main # echo "8:23:respawn:/usr/sbin/chroot /sid-root /sbin/getty 38400 tty8"  >> /etc/inittab
main # init q
  • reload init

10.8.3. Setting up X for chroot

You want to run the latest X and GNOME safely in your chroot? That's entirely possible! The following example will make GDM run on virtual terminal vt9.

First install a chroot system. From the root of the main system, copy key configuration files to the chroot system.

main # cp /etc/X11/xorg.conf /sid-root/etc/X11/xorg.conf
main # chroot /sid-root
chroot # cd /dev; /sbin/MAKEDEV generic ; cd -
chroot # aptitude install gdm gnome x-window-system
chroot # vim /etc/gdm/gdm.conf
  • change "[servers]" section with "s/vt7/vt9/" to make the first virtual console in the chroot from vt7 to vt9.

chroot # /etc/init.d/gdm start

Now you can easily switch back and forth between full X environments in your chroot and your main system just by switching between Linux virtual terminals; e.g. by using Ctrl-Alt-F7 and Ctrl-Alt-F9. Have fun!

10.8.4. Run other distributions with chroot

A chroot environment for another Linux distribution can easily be created. You install a system into separate partitions using the installer of the other distribution. If its root partition is in /dev/hda9:

main # cd / ; mkdir /other-dist
main # mount -t ext3 /dev/hda9 /other-dist
main # chroot /other-dist /bin/bash

10.8.5. Build packages under chroot

There is a more specialized chroot package, pbuilder, which constructs a chroot system and builds a package inside the chroot. It is an ideal system to use to check that a package's build-dependencies are correct, and to be sure that unnecessary and wrong build dependencies will not exist in the resulting package.

10.8.6. Other virtualization tools

There are several system virtualization and emulation related packages in Debian beyond simple chroot.

Table 10.22.  List of virtualization tools

package

pocon

size

description

schroot

V:1.0, I:1.7

1900

Specialized tool for executing Debian binary packages in chroot

sbuild

V:0.08, I:0.3

452

Tool for building Debian binary packages from Debian sources

pbuilder

V:0.5, I:2

1116

Personal package builder for Debian packages

debootstrap

V:1.5, I:12

260

Bootstrap a basic Debian system (written in sh)

cdebootstrap

V:0.6, I:3

156

Bootstrap a Debian system (written in C)

rootstrap

V:0.04, I:0.2

156

A tool for building complete Linux filesystem images

user-mode-linux

V:0.11, I:0.5

17816

User-mode Linux (kernel)

xen-tools

V:0.2, I:1.9

996

Tools to manage debian XEN virtual server

bochs

V:0.08, I:0.6

3072

Bochs: IA-32 PC emulator

qemu

V:0.8, I:6

30752

Qemu: fast generic processor emulator

virtualbox-ose

V:2, I:2

22272

VirtualBox: x86 virtualization solution on i386 and amd64

wine

V:2, I:15

96

Wine: Windows API Implementation (standard suite)

dosbox

V:0.6, I:3

2240

DOSBox: x86 emulator with Tandy/Herc/CGA/EGA/VGA/SVGA graphics, sound and DOS

util-vserver

V:0.6, I:1.0

2928

Linux-VServer virtual private servers - user-space tools

vzctl

V:0.3, I:0.7

1120

OpenVZ server virtualization solution - control tools

vzquota

V:0.3, I:0.7

272

OpenVZ server virtualization solution - quota tools


See Wikipedia article http://en.wikipedia.org/wiki/Comparison_of_virtual_machines for detail comparison of different virtualization solutions.