Archives pour 11/2016

HP-41C Synthetic Programming

23/11/2016 Comments off


Many of these instructions were intentionally left out because used incorrectly they can confuse the calculator and cause either a lockup or a « Memory Lost » state. (If you get into the former state, you may need to remove the batteries to reset the calculator.)

You should backup anything important before first engaging in Synthetic Programming.

How Synthetic Instructions Work

HP-41 instructions are one or more bytes long. The calculator will only allow certain sequences, but with the tool below, you’ll be able create new sequences by entering code that the calculator allows and then grabbing bytes out of this code to create different instructions. These new sequences allow access to additional characters, additional sounds, more alpha editing commands, easy control of the calculator through direct access to system registers, etc. They make it possible to do new things and to reduce the size and execution time of programs. The byte grabber described below will allow you to remove individual bytes from programs you create so the the bytes that remain are interpreted differently.

Creating a Byte Grabber

You can use the following steps to create a Byte Grabber. Make sure to follow the steps exactly. If it doesn’t work the first time, try again. Note that the first step is a master clear so save anything important to cards, tape, or disk now!

  1. Remove any accessory modules.
  2. Do a Master clear by holding down the backspace key while turning on the calculator. The Display will show MEMORY LOST.
  3. Assign « + » to the LN key by pressing shift ASN ALPHA shift + ALPHA LN.
  4. Assign « DEL » to the LOG key by pressing shift ASN ALPHA D E L ALPHA LOG.
  5. Press PRGM to witch to program mode. The display should show 00 REG 45.
  6. Start catalog 1 by pressing shift CATALOG 1 and press R/S immediately before the display blinks. If the display blinks, you waited too long. Repeat this step as many times as necessary to get the R/S pressed before the display blinks. (The display will show the .END. instruction both before and after the blink, but you must press R/S before the blink.)
  7. Press the ALPHA key to go into Alpha mode.
  8. Press the backspace key. The display should now show 4094 RCL 01.
  9. Press ALPHA to leave Alpha mode.
  10. Press shift GTO .005 and you should see 05 LBL 03.
  11. Press USER (if necessary) to enter User mode.
  12. Press LOG 003 which uses the assignment you made earlier to DEL 3 steps. You should now see 04 STO 01.
  13. Press ALPHA to go back into Alpha mode.
  14. Press ? A A A A A A (Everything after the first A will probably display as « -« s.) Press exactly 6 A’s!
  15. Press PRGM to leave program mode and ALPHA to leave Alpha mode.
  16. Press shift GTO . . (press both dots)

The byte grabber should now be assigned to the LN key. Press AND HOLD the LN key which should display XROM 28,63. Keep holding the key until the calculator displays NULL because you don’t want to execute the byte grabber now. This would be a good time to save the calculator’s status on a card by pressing XEQ ALPHA W S T S ALPHA in case you accidentally destroy the byte grabber later.

Be careful in using the byte grabber. You may get a « MEMORY LOST » or lock the calculator if you use it incorrectly. If the latter happens, remove the batteries for a few seconds and return them. If that doesn’t work, try turning the calculator on a few times with the batteries out or leave them out for several hours. Lire la suite…

How to Enable IP Forwarding in Linux

19/11/2016 Comments off

ip forwarding linuxBy default any modern Linux distributions will have IP Forwarding disabled. This is normally a good idea, as most peoples will not need IP Forwarding, but if we are setting up a Linux router/gateway or maybe a VPN server (pptp or ipsec) or just a plain dial-in server then we will need to enable forwarding. This can be done in several ways that I will present bellow.

Check if IP Forwarding is enabled

We have to query the sysctl kernel value net.ipv4.ip_forward to see if forwarding is enabled or not: Using sysctl:

sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0

or just checking out the value in the /proc system:

cat /proc/sys/net/ipv4/ip_forward

As we can see in both the above examples this was disabled (as show by the value 0).

Enable IP Forwarding on the fly

As with any sysctl kernel parameters we can change the value of net.ipv4.ip_forward on the fly (without rebooting the system):

sysctl -w net.ipv4.ip_forward=1


echo 1 > /proc/sys/net/ipv4/ip_forward

the setting is changed instantly; the result will not be preserved after rebooting the system.

Permanent setting using /etc/sysctl.conf

If we want to make this configuration permanent the best way to do it is using the file /etc/sysctl.conf where we can add a line containing net.ipv4.ip_forward = 1

net.ipv4.ip_forward = 1

if you already have an entry net.ipv4.ip_forward with the value 0 you can change that 1.

To enable the changes made in sysctl.conf you will need to run the command:

sysctl -p /etc/sysctl.conf

On RedHat based systems this is also enabled when restarting the network service:

service network restart

and on Debian/Ubuntu systems this can be also done restarting the procps service:

/etc/init.d/ restart

Using distribution specific init scripts

Although the methods presented above should work just fine and you would not need any other method of doing this, I just wanted to note that there are also other methods to enable IP Forwarding specific to some Linux distributions. For example Debian based distributions might use the setting:


set it to yes and restart the network service. Also RedHat distributions might set this using:


and again restart the network service.

Regardless the method you have used once you have completed this you can check it out using the same method shown above:

sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1

cat /proc/sys/net/ipv4/ip_forward

If the result is 1 then the Linux system will start forwarding IP packets even if they are not destined to any of its own network interfaces.

Categories: Réseau Tags:

HowTo: The Ultimate Logrotate Command Tutorial with 10 Examples

12/11/2016 Comments off

Managing log files effectively is an essential task for Linux sysadmin.

In this article, let us discuss how to perform following log file operations using UNIX logrotateutility.

  • Rotate the log file when file size reaches a specific size
  • Continue to write the log information to the newly created file after rotating the old log file
  • Compress the rotated log files
  • Specify compression option for the rotated log files
  • Rotate the old log files with the date in the filename
  • Execute custom shell scripts immediately after log rotation
  • Remove older rotated log files

1. Logrotate Configuration files

Following are the key files that you should be aware of for logrotate to work properly.

/usr/sbin/logrotate – The logrotate command itself.

/etc/cron.daily/logrotate – This shell script executes the logrotate command everyday.

$ cat /etc/cron.daily/logrotate

/usr/sbin/logrotate /etc/logrotate.conf
if [ $EXITVALUE != 0 ]; then
    /usr/bin/logger -t logrotate "ALERT exited abnormally with [$EXITVALUE]"
exit 0

/etc/logrotate.conf – Log rotation configuration for all the log files are specified in this file.


$ cat /etc/logrotate.conf
rotate 4
include /etc/logrotate.d
/var/log/wtmp {
    minsize 1M
    create 0664 root utmp
    rotate 1

/etc/logrotate.d – When individual packages are installed on the system, they drop the log rotation configuration information in this directory. For example, yum log rotate configuration information is shown below.

$ cat /etc/logrotate.d/yum
/var/log/yum.log {
    size 30k
    create 0600 root root

2. Logrotate size option: Rotate the log file when file size reaches a specific limit

If you want to rotate a log file (for example, /tmp/output.log) for every 1KB, create the logrotate.conf as shown below.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        create 700 bala bala
        rotate 4

This logrotate configuration has following three options:

  • size 1k – logrotate runs only if the filesize is equal to (or greater than) this size.
  • create – rotate the original file and create the new file with specified permission, user and group.
  • rotate – limits the number of log file rotation. So, this would keep only the recent 4 rotated log files.

Before the logrotation, following is the size of the output.log:

$ ls -l /tmp/output.log
-rw-r--r-- 1 bala bala 25868 2010-06-09 21:19 /tmp/output.log

Now, run the logrotate command as shown below. Option -s specifies the filename to write the logrotate status.

$ logrotate -s /var/log/logstatus logrotate.conf

Note : whenever you need of log rotation for some files, prepare the logrotate configuration and run the logroate command manually.
After the logrotation, following is the size of the output.log:

$ ls -l /tmp/output*
-rw-r--r--  1 bala bala 25868 2010-06-09 21:20 output.log.1
-rwx------ 1 bala bala        0 2010-06-09 21:20 output.log

Eventually this will keep following setup of rotated log files.

  • output.log.4.
  • output.log.3
  • output.log.2
  • output.log.1
  • output.log

Please remember that after the log rotation, the log file corresponds to the service would still point to rotated file (output.log.1) and keeps on writing in it. You can use the above method, if you want to rotate the apache access_log or error_log every 5 MB.

Ideally, you should modify the /etc/logrotate.conf to specify the logrotate information for a specific log file.

Also, if you are having huge log files, you can use: 10 Awesome Examples for Viewing Huge Log Files in Unix

3. Logrotate copytruncate option: Continue to write the log information in the newly created file after rotating the old log file.

$ cat logrotate.conf
/tmp/output.log {
         size 1k
         rotate 4

copytruncate instruct logrotate to creates the copy of the original file (i.e rotate the original log file) and truncates the original file to zero byte size. This helps the respective service that belongs to that log file can write to the proper file.

While manipulating log files, you might find the sed substitutesed delete tips helpful.

4. Logrotate compress option: Compress the rotated log files

If you use the compress option as shown below, the rotated files will be compressed with gzip utility.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        create 700 bala bala
        rotate 4

Output of compressed log file:

$ ls /tmp/output*
output.log.1.gz output.log

5. Logrotate dateext option: Rotate the old log file with date in the log filename

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        create 700 bala bala
        rotate 4

After the above configuration, you’ll notice the date in the rotated log file as shown below.

$ ls -lrt /tmp/output*
-rw-r--r--  1 bala bala 8980 2010-06-09 22:10 output.log-20100609.gz
-rwxrwxrwx 1 bala bala     0 2010-06-09 22:11 output.log

This would work only once in a day. Because when it tries to rotate next time on the same day, earlier rotated file will be having the same filename. So, the logrotate wont be successful after the first run on the same day.

Typically you might use tail -f to view the output of the log file in realtime. You can even combine multiple tail -f output and display it on single terminal.

6. Logrotate monthly, daily, weekly option: Rotate the log file weekly/daily/monthly

For doing the rotation monthly once,

$ cat logrotate.conf
/tmp/output.log {
        rotate 4

Add the weekly keyword as shown below for weekly log rotation.

$ cat logrotate.conf
/tmp/output.log {
        rotate 4

Add the daily keyword as shown below for every day log rotation. You can also rotate logs hourly.

$ cat logrotate.conf
/tmp/output.log {
        rotate 4

7. Logrotate postrotate endscript option: Run custom shell scripts immediately after log rotation

Logrotate allows you to run your own custom shell scripts after it completes the log file rotation. The following configuration indicates that it will execute after the logrotation.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        rotate 4

8. Logrotate maxage option: Remove older rotated log files

Logrotate automatically removes the rotated files after a specific number of days.  The following example indicates that the rotated log files would be removed after 100 days.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        rotate 4
        maxage 100

9. Logrotate missingok option: Dont return error if the log file is missing

You can ignore the error message when the actual file is not available by using this option as shown below.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        rotate 4

10. Logrotate compresscmd and compressext option: Sspecify compression command for the log file rotation

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        compresscmd /bin/bzip2
        compressext .bz2
        rotate 4

Following compression options are specified above:

  • compress – Indicates that compression should be done.
  • compresscmd – Specify what type of compression command should be used. For example: /bin/bzip2
  • compressext – Specify the extension on the rotated log file. Without this option, the rotated file would have the default extension as .gz. So, if you use bzip2 compressioncmd, specify the extension as .bz2 as shown in the above example.
Categories: Système, Tutoriel Tags:

How can I find out if a specific program is installed?

07/11/2016 Comments off

there’s always apt-cache policy <package-name> (no sudo needed).

Not installed:

olivier@neews:/$ apt-cache policy gnuift
   Installed: (none)
   Candidate: 0.1.14-11
   Version table:
      0.1.14-11 0
         500 oneiric/universe amd64 Packages


olivier@neews:/$ apt-cache policy firefox
   Installed: 8.0+build1-0ubuntu0.11.10.3
   Candidate: 8.0+build1-0ubuntu0.11.10.3
   Version table:
  *** 8.0+build1-0ubuntu0.11.10.3 0
         500 oneiric-updates/main amd64 Packages
         500 oneiric-security/main amd64 Packages
         100 /var/lib/dpkg/status
      7.0.1+build1+nobinonly-0ubuntu2 0
         500 oneiric/main amd64 Packages

Or dpkg: dpkg -l | grep -E '^ii' | grep <package name>. When it’s not installed it won’t show output. When it is, it’ll show something like:

olivier@neews:~$ dpkg -l | grep -E '^ii' | grep firefox
 ii  firefox                                                     8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla
 ii  firefox-branding                                            8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - transitional package
 ii  firefox-globalmenu                                          8.0+build1-0ubuntu0.11.10.3                            Unity appmenu integration for Firefox
 ii  firefox-gnome-support                                       8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - GNOME support
 ii  firefox-locale-en                                           8.0+build1-0ubuntu0.11.10.3                            English language pack for Firefox
It's obviously a fuzzier search but handy if you're not sure which package you're looking for.
 For manually installed things...
 A bit harder but if they're on the current path, you could just run them. That's a bit of mission so I'd rather just run:
 oli@bert:/$ which chromium-browser


oli@bert:/$ which gnuift
# returns nothing

Which is better?

That depends on the sanity of user. There’s nothing to stop somebody installing something called chromium-browser that isn’t Chromium. They could even package it up incorrectly and install that. Neither method can be 100% certain.

But assuming the owner is sane – packages should be good enough for most people.

Categories: Système Tags: , , ,

How do I replicate installed package selections from one Debian system to another? (Debian Wheezy)

07/11/2016 Comments off

To clone a Debian installation, use the apt-clone utility. It’s available (as a separate package, not part of the default installation) in Debian since wheezy and in Ubuntu since 12.04. On the existing machine, run

apt-clone clone foo

This creates a file foo.apt-clone.tar.gz. Copy it to the destination machine, and run

apt-get install apt-clone
apt-clone restore foo.apt-clone.tar.gz

If you’re working with an old system where apt-clone isn’t available, or if you just want to replicate the list of installed packages but not any configuration file, here are the manual steps.

  • On the source machine:
cat /etc/apt/sources.list /etc/apt/sources.list.d >sources.list
pkg --get-selections >selections.list
apt-mark auto >auto.list
  • On the target machine:
cp sources.list /etc/apt/
apt-get update
/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/
dpkg --set-selections <selections.list
apt-get dselect-upgrade
xargs apt-mark auto <auto.list

I believe that you’re affected by an incompatible change in dpkg that first made it into wheezy. See bug #703092 for background.

The short story is that dpkg --set-selections now only accepts package names that are present in the file /var/lib/dpkg/status or /var/lib/dpkg/available. If you only use APT to manage packages, like most people, then /var/lib/dpkg/available is not kept up-to-date.

After running apt-get update and before running dpkg --set-selections and apt-get -u dselect-upgrade, run the following command:

apt-cache dumpavail >/tmp/apt.avail
dpkg --merge-avail /tmp/apt.avail

From jessie onwards, you can simplify this to

apt-cache dumpavail | dpkg --merge-avail

Alternatively, run

/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/

or even simpler

apt-get install dctrl-tools

Another simple method that doesn’t require installing an additional package but will download the package lists again is

dselect update

See the dpkg FAQ for more information. (This is mentioned in the dpkg man page, but more in a way that would remind you of the issue if you were already aware, not in a way that explains how to solve the problem!)

Note that cloning a package installation with dpkg --set-selections doesn’t restore the automatic/manual mark in APT. See Restoring all data and dependencies from dpkg –set-selections ‘*’ for more details. You can save the marks on the source system with

apt-mark showauto >auto.list

and restore them on the target system with

xargs apt-mark auto <auto.list
Categories: Système Tags: , ,