When I boot my machine it shows all generations in a list, but naming them "Generation 49", "Generation 50", etc.
Is there a way to add labels to generations, so that I can easily see later what was changed? I'd like to have something like an optional commit message, so it could be like "Generation 49 - switched to KDE5", "Generation 50 - switched back to gnome3".
/boot/grub/grub.conf is currently built from:
nixos/modules/system/boot/loader/grub/install-grub.pl
# Emit submenus for all system profiles.
sub addProfile {
my ($profile, $description) = #_;
# Add entries for all generations of this profile.
$conf .= "submenu \"$description\" {\n" if $grubVersion == 2;
sub nrFromGen { my ($x) = #_; $x =~ /\/\w+-(\d+)-link/; return $1; }
my #links = sort
{ nrFromGen($b) <=> nrFromGen($a) }
(glob "$profile-*-link");
my $curEntry = 0;
foreach my $link (#links) {
last if $curEntry++ >= $configurationLimit;
my $date = strftime("%F", localtime(lstat($link)->mtime));
my $version =
-e "$link/nixos-version"
? readFile("$link/nixos-version")
: basename((glob(dirname(Cwd::abs_path("$link/kernel")) . "/lib/modules/*"))[0]);
addEntry("NixOS - Configuration " . nrFromGen($link) . " ($date - $version)", $link);
}
$conf .= "}\n" if $grubVersion == 2;
}
this is a single entry in grub.conf:
menuentry "NixOS - Configuration 38 (2016-01-29 - 16.03pre75806.77f8f35)" {
search --set=drive1 --fs-uuid d931bd85-8f35-4ae9-a36b-c1ac51ad7b57
linux ($drive1)//kernels/56fkcbxnwzi0kh6vg677a4cd4zcabm55-linux-4.1.15-bzImage systemConfig=/nix/store/2sybsl278s5a8kzhplwcz5jbhbsqwdci-nixos-system-lenovo-t530-16.03pre75806.77f8f35 init=/nix/store/2sybsl278s5a8kzhplwcz5jbhbsqwdci-nixos-system-lenovo-t530-16.03pre75806.77f8f35/init loglevel=4
initrd ($drive1)//kernels/r33fajk0kaxlfmg922c2hy4rak5cj90z-initrd-initrd
}
however, nixos-rebuild supports --profile-name, quoting the manpage:
--profile-name, -p
Instead of using the Nix profile /nix/var/nix/profiles/system to keep track of
the current and previous system configurations, use
/nix/var/nix/profiles/system-profiles/name. When you use GRUB 2, for every
system profile created with this flag, NixOS will create a submenu named “NixOS
- Profile 'name'” in GRUB’s boot menu, containing the current and previous
configurations of this profile.
For instance, if you want to test a configuration file named test.nix without
affecting the default system profile, you would do:
$ nixos-rebuild switch -p test -I nixos-config=./test.nix
The new configuration will appear in the GRUB 2 submenu “NixOS - Profile
'test'”.
summary: hope this is what you are looking for.
NIXOS_LABEL="changed-some-settings" nixos-rebuild switch
system.nixos.label
You can set it either in your config, or in the environment (using NIXOS_LABEL).
Related
I set up a crontab. I've installed AIDE and I have an AIDE database to check for file integrity.
How do I get cron to email me ONLY when files have been modified?
The script:
#!/bin/bash
if aide -c /etc/aide/aide.conf --check
then echo "AIDE detected no changes"
else
echo "Alert!: AIDE detected changes!"
The crontab:
* */12 * * * /root/script.sh | mail root#localhost.com
Use the MAILTO crontab variable rather then piping to mail. Then change your script so that it doesn't output anything unless there is a problem:
#!/bin/bash
aide -c /etc/aide/aide.conf --check || echo "Alert!: AIDE detected changes!"
The crontab:
MAILTO=root#localhost.com
* */12 * * * /root/script.sh
MAILTO=""
Notes:
You can use a simple (local) username instead; e.g. root.
You need to have set up mail handling on your system; e.g. delivery to local mailboxes or relaying via an external SMTP serice provider such as Gmail. That is beyond the scope of this Q&A.
The MAILTO="" is to stop following cron rules from sending mails. If you want them to do that, leave it out. It must be MAILTO="" not MAILTO=. (Cron is not implementing shell syntax here. Another clue is that the you can put spaces around the = which you can't do with shell syntax.)
Setting of variables in crontab is not part of the POSIX spec. There have been many implementations of cron over the years and not all of them support variable setting. Check what man 5 crontab says on your system.
Alternatively, you could use ... | mailx -E root#localhost.com rather than ... | mail root#localhost.com. This will skip sending the mail if the body (i.e. stdin) is empty.
How do I get cron to email me ONLY when files have been modified?
If you are on Linux with a local file system (e.g. ext4(5) or BTRFS), consider using inotify(7) facilities and then install incrond (on Debian or Ubuntu: the incron package) and use incrontab(5).
Be aware that incron and inotify don't work on remote file systems such as NFS or SMB/CIFS or on pseudofile systems like proc(5).
If you cannot use incron you'll need to use find(1) and perhaps stat(1) in your shell script periodically called by cron
BTW, some files (e.g. those under /var/run/, see hier(7) for more) are very often modified. And so are the data files handled by RDBMS such as PostGreSQL
Regarding AIDE, be sure to read its documentation. Since it is open source and even free software, consider studying then improving its code (e.g. to use inotify).
We wrote a Perl script that sends out an email if something went wrong and updates the database so that this email won't go out again.
#!/usr/bin/perl
my $aide = "/usr/sbin/aide -c /etc/aide.conf";
my $email = "security\#your-domain.com";
my $timestamp = `/bin/date +\%Y-\%m-\%d.\%H-\%M`;
my $output = "";
my $added = -1;
my $removed = -1;
my $changed = -1;
my $warning = 0;
my $found_no_differences = 0;
open(AIDE, "$aide --check|");
while (my $line=<AIDE>) {
chomp($line);
$output = $output.$line."\n";
if ($line =~ /Added entries\:\s*(\w+)/) { $added = $1; }
if ($line =~ /Removed entries\:\s*(\w+)/) { $removed = $1; }
if ($line =~ /Changed entries\:\s*(\w+)/) { $changed = $1; }
if ($line =~ /WARNING\:/) { $warning = $warning + 1; }
if ($line =~ /AIDE found NO differences/) { $found_no_differences = 1; }
}
close(AIDE);
if ($found_no_differences > 0) { exit(0); }
if ($added > 0 || $removed > 0 || $changed > 0 || $warning > 0 || $added == -1 || $changed == -1) {
open MAIL, "|mail -s 'AIDE $timestamp' $email";
print MAIL $output;
close MAIL;
system("$aide --init");
system("mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz");
}
by default aide sends email to local root user, it's probably best to create an alias for the local root user to noc#domain.com or whatever you use for your incoming email address, this way you not only get aide emails but also other system mail that's destined for the user root
The following Perl script generates an .xls file from a text file. It runs great in our linux test environment, but generates an empty spreadsheet (.xls) in our production environment when run via cron (cron works in test, as well.) Nothing jumps out at our sys admins in terms of system level settings that might account for this behavior. Towards the bottom of the script in the import_data subroutine, the correct number of lines is reported, but nothing is written to the spreadsheet and no errors are returned at either the script or system level. I ran it through the perl debugger but my skills fell short of being able to interactively watch it populate the file. The cron entry looks like this:
cd <script directory>; cvs2xls input.txt output.xls 2>&1
Any debugging tips would be appreciated, as well as potential system settings that I can forward on to our sysadmins.
#!/usr/bin/perl
use strict;
use warnings;
use lib '/apps/tu01688/perl5/lib/perl5';
use Spreadsheet::WriteExcel;
use Text::CSV::Simple;
BEGIN {
unshift #INC, "/apps/tu01688/jobs/mayo-expert";
};
my $infile = shift;
usage() unless defined $infile && -f $infile;
my $parser = Text::CSV::Simple->new;
my #data = $parser->read_file($infile);
my $headers = shift #data;
my $outfile = shift || $infile . ".xls";
my $subject = shift || 'worksheet';
sub usage {
print "csv2xls infile [outfile] [subject]\n";
exit;
}
my $workbook = Spreadsheet::WriteExcel->new($outfile);
my $bold = $workbook->add_format();
$bold->set_bold(1);
import_data($workbook, $subject, $headers, \#data);
# Add a worksheet
sub import_data {
my $workbook = shift;
my $base_name = shift;
my $colums = shift;
my $data = shift;
my $limit = shift || 50_000;
my $start_row = shift || 1;
my $worksheet = $workbook->add_worksheet($base_name);
$worksheet->add_write_handler(qr[\w], \&store_string_widths);
#$worksheet->add_write_handler(qr[\w]| \&store_string_widths);
my $w = 1;
$worksheet->write('A' . $start_row, $colums, ,$bold);
my $i = $start_row;
my $qty = 0;
for my $row (#$data) {
$qty++;
if ($i > $limit) {
$i = $start_row;
$w++;
$worksheet = $workbook->add_worksheet("$base_name - $w");
$worksheet->write('A1', $colums,$bold);
}
$worksheet->write($i++, 0, $row);
}
autofit_columns($worksheet);
warn "Converted $qty rows.";
return $worksheet;
}
###############################################################################
###############################################################################
#
# Functions used for Autofit.
#
###############################################################################
#
# Adjust the column widths to fit the longest string in the column.
#
sub autofit_columns {
my $worksheet = shift;
my $col = 0;
for my $width (#{$worksheet->{__col_widths}}) {
$worksheet->set_column($col, $col, $width) if $width;
$col++;
}
}
###############################################################################
#
# The following function is a callback that was added via add_write_handler()
# above. It modifies the write() function so that it stores the maximum
# unwrapped width of a string in a column.
#
sub store_string_widths {
my $worksheet = shift;
my $col = $_[1];
my $token = $_[2];
# Ignore some tokens that we aren't interested in.
return if not defined $token; # Ignore undefs.
return if $token eq ''; # Ignore blank cells.
return if ref $token eq 'ARRAY'; # Ignore array refs.
return if $token =~ /^=/; # Ignore formula
# Ignore numbers
#return if $token =~ /^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/;
# Ignore various internal and external hyperlinks. In a real scenario
# you may wish to track the length of the optional strings used with
# urls.
return if $token =~ m{^[fh]tt?ps?://};
return if $token =~ m{^mailto:};
return if $token =~ m{^(?:in|ex)ternal:};
# We store the string width as data in the Worksheet object. We use
# a double underscore key name to avoid conflicts with future names.
#
my $old_width = $worksheet->{__col_widths}->[$col];
my $string_width = string_width($token);
if (not defined $old_width or $string_width > $old_width) {
# You may wish to set a minimum column width as follows.
#return undef if $string_width < 10;
$worksheet->{__col_widths}->[$col] = $string_width;
}
# Return control to write();
return undef;
}
###############################################################################
#
# Very simple conversion between string length and string width for Arial 10.
# See below for a more sophisticated method.
#
sub string_width {
return length $_[0];
}
Uhmm.. don't put chained commands in cron, use an external script instead. Anyway: some suggestions that may help you:
Debugging cron commands
Check the mail! By default cron will mail any output from the command to the user it is running the command as. If there is no output there will be no mail. If you want cron to send mail to a different account then you can set the MAILTO environment variable in the crontab file e.g.
MAILTO=user#somehost.tld
1 2 * * * /path/to/your/command
Capture the output yourself
1 2 * * * /path/to/your/command &>/tmp/mycommand.log
which captures stdout and stderr to /tmp/mycommand.log
Look at the logs; cron logs its actions via syslog, which (depending on your setup) often go to /var/log/cron or /var/log/syslog.
If required you can filter the cron statements with e.g.
grep CRON /var/log/syslog
Now that we've gone over the basics of cron, where the files are and how to use them let's look at some common problems.
Check that cron is running
If cron isn't running then your commands won't be scheduled ...
ps -ef | grep cron | grep -v grep
should get you something like
root 1224 1 0 Nov16 ? 00:00:03 cron
or
root 2018 1 0 Nov14 ? 00:00:06 crond
If not restart it
/sbin/service cron start
or
/sbin/service crond start
There may be other methods; use what your distro provides.
cron runs your command in a restricted environment.
What environment variables are available is likely to be very limited. Typically, you'll only get a few variables defined, such as $LOGNAME, $HOME, and $PATH.
Of particular note is the PATH is restricted to /bin:/usr/bin. The vast majority of "my cron script doesn't work" problems are caused by this restrictive path. If your command is in a different location you can solve this in a couple of ways:
Provide the full path to your command.
1 2 * * * /path/to/your/command
Provide a suitable PATH in the crontab file
PATH=/usr:/usr/bin:/path/to/something/else
1 2 * * * command
If your command requires other environment variables you can define them in the crontab file too.
cron runs your command with cwd == $HOME
Regardless of where the program you execute resides on the filesystem, the current working directory of the program when cron runs it will be the user's home directory. If you access files in your program, you'll need to take this into account if you use relative paths, or (preferably) just use fully-qualified paths everywhere, and save everyone a whole lot of confusion.
The last command in my crontab doesn't run
Cron generally requires that commands are terminated with a new line. Edit your crontab; go to the end of the line which contains the last command and insert a new line (press enter).
Check the crontab format
You can't use a user crontab formatted crontab for /etc/crontab or the fragments in /etc/cron.d and vice versa. A user formatted crontab does not include a username in the 6th position of a row, while a system formatted crontab includes the username and runs the command as that user.
I put a file in /etc/cron.{hourly,daily,weekly,monthly} and it doesn't run
Check that the filename doesn't have an extension see run-parts
Ensure the file has execute permissions.
Tell the system what to use when executing your script (eg. put #!/bin/sh at top)
Cron date related bugs
If your date is recently changed by a user or system update, timezone or other, then crontab will start behaving erratically and exhibit bizarre bugs, sometimes working, sometimes not. This is crontab's attempt to try to "do what you want" when the time changes out from underneath it. The "minute" field will become ineffective after the hour is changed. In this scenario, only asterisks would be accepted. Restart cron and try it again without connecting to the internet (so the date doesn't have a chance to reset to one of the time servers).
Percent signs, again
To emphasise the advice about percent signs, here's an example of what cron does with them:
# cron entry
* * * * * cat >$HOME/cron.out%foo%bar%baz
will create the ~/cron.out file containing the 3 lines
foo
bar
baz
This is particularly intrusive when using the date command. Be sure to escape the percent signs
* * * * * /path/to/command --day "$(date "+\%Y\%m\%d")"
Thanks so much for the extensive feedback, everyone. I'm certainly taking a lot more away from this than I put into it. In any event, I ran across the answer. In my perl5 lib folder I found that somehow the IO and OLE libraries were missing on production. Copying those over from development resulted in everything working fine. The fact that I was unable to determine/capture this through conventional debugging efforts as opposed to merely comparing directory listings out of exasperation speaks to how much more I have to learn along these lines. But I'm confident that the great feedback I received will go a long ways towards getting me there. Thanks again, everyone.
File services - contains many records like this one:
define service {
host_name\t\t\t\tHOSTNAME
...
...
}
File hosts - contains records:
define host {
host_name\t\t\t\tHOSTNAME
...
...
}
and I need to go to hosts, somehow get name of HOSTNAME from first record, then go to file services and find all records with that HOSTNAME and put them to other file. Then do it for every HOSTNAME in hosts.
What I don't know is primary how to get the HOSTNAME from file hosts and then how to get a whole record in file services to a variable. I have prepared a regex (hope it's right) ^define.*host_name\t\t\t\t$HOSTNAME.*}
Please give me a few advices or examples how to get wanted result.
The files you provide look very much like nagios configuration files.
sed might be your friend here, as it allows you to slice the file into smaller parts, eg:
:t
/^define service {/,/}$/ { # For each line between these block markers..
/}$/!{ # If we are not at the /end/ marker
$!{ # nor the last line of the file,
N; # add the Next line to the pattern space
bt
} # branch (loop back) to the :t label.
} # This line matches the /end/ marker.
/host_name[ \t]\+HOSTNAME\b/!d; # delete the block if wrong host.
}
That example lifted from the sed faq 4.21, and adapted slightly. You could also look at question 4.22 which appears to address this directly:
http://sed.sourceforge.net/sedfaq4.html#s4.22
Like the previous answer, I'm also inclined to say you're probably better off using another scripting language. If you need a different interpreter to get this done anyway, might as well use something you know.
This task a bit too complex for a bash script. I would use Perl:
#!/usr/bin/perl
use warnings;
use strict;
open my $SRV, '<', 'services' or die $!;
open my $HST, '<', 'hosts' or die $!;
my %services;
{ local $/ = "\n}";
while (my $service = <$SRV>) {
my ($hostname) = $service =~ /^\s*host_name\t+(.+?)\s*$/m;
push #{ $services{$hostname} }, $service if defined $hostname;
}
}
while (my $line = <$HST>) {
if (my ($host) = $line =~ /^\s*host_name\t+(.+?)\s*$/) {
if (exists $services{$host}) {
print "===== $host =====\n";
print "$_\n" for #{ $services{$host} };
} else {
warn "$host not found in services!\n";
}
}
}
I have a perl script running as root, and from within it I want to execute a system command bar as a lesser priveleged user foo. So I have my system call wrapped as follows:
sub dosys
{
system(#_) == 0
or die "system #_ failed: $?";
}
And so I want to say:
as user foo dosys("bar")
Is there a mechanism within perl or the underlying bash shell that I can use to do this? (I would prefer one that didn't require installing an additional cpan library if possible)
The POSIX module is a Perl core module, and it includes the functions:
setuid()
setgid()
and related get*id() functions, though the values are also available through special variables:
$) and $( (effective and real GID)
$< and $> (effective and real UID)
You can also try setting those directly (per $EGID and $UID).
system('su www-data -c whoami')
> www-data
You have to change groups first, remember to quash supplementary groups, and then change user. You'll want to do this in a separate process, so that the [UG]ID changing doesn't affect privs on your root process.
sub su_system {
my $acct = shift;
my $gid = getgrnam $acct; # XXX error checking!
my $uid = getpwnam $acct;
if (fork) { # XXX error checking!
wait;
return $? >> 8;
}
# -- child
$( = $) = "$gid $gid"; # No supp. groups; see perlvar $)
$< = $> = $uid;
exec #_; # XXX not as safe as exec {prog} #argv
# oh, and what if $acct had [ug]id zero? darn
}
Proceed with caution.
Situation: I'm using multiple monitors and I want to get their names in bash. Currently I'm using Ubuntu 10.04.
I know about xrandr. From it I can get only statistics data. What I want is to read all monitor names in an array to work with them.
Is there a clear way to do that without cutting names from some kind of string? A clear way would be reading them from file. A not clear way would be to pipe xrandr output to some sort a function to cut names out from it.
Inspired by Beni's answer, this will read the EDID data using xrandr and extract the monitors names according to the EDID specification, with no need of any external tools like parse-edid:
#!/bin/bash
while read -r output hex conn; do
[[ -z "$conn" ]] && conn=${output%%-*}
echo "# $output $conn $(xxd -r -p <<< "$hex")"
done < <(xrandr --prop | awk '
!/^[ \t]/ {
if (output && hex) print output, hex, conn
output=$1
hex=""
}
/ConnectorType:/ {conn=$2}
/[:.]/ && h {
sub(/.*000000fc00/, "", hex)
hex = substr(hex, 0, 26) "0a"
sub(/0a.*/, "", hex)
h=0
}
h {sub(/[ \t]+/, ""); hex = hex $0}
/EDID.*:/ {h=1}
END {if (output && hex) print output, hex, conn}
' | sort
)
Uses awk to precisely extract the monitor name only, and no extra garbage from the EDID, hence "magic numbers" like 000000fc00, 26 and 0a. Finally uses xxd to convert from hex to ASCII, printing one monitor name per line.
Based on this solution I made a handy script to switch monitors, which can also be used to simply list monitor info:
$ monitor-switch --list
Connected monitors:
# DFP5 HDMI HT-R391
# DFP7 DVI-I DELL U2412M
$ monitor-switch --list
Connected monitors:
# DisplayPort-1 DisplayPort DELL U2412M
# DisplayPort-3 DisplayPort DELL U2415
# HDMI-A-2 HDMI LG TV
Tested on Ubuntu 16.04, 18.04. (I know its too late to answer but this solution is relevant today)
$ sudo apt-get install -y hwinfo
...
$ hwinfo --monitor --short
monitor:
SONY TV
AUO LCD Monitor
I have two monitors attached. One with the laptop and the other is an external display. As soon as the external monitor is plugged-in or out, this command reflects the change. You continuously need to poll. Removing the --short option gives more detailed information.
You can poll the state with the following background job:
$ while true;
> do
> hwinfo --monitor --short;
> sleep 2;
> done >> monitor.log &
The while true loop runs infinite times. The sleep 2 pauses each iteration of the loop for 2 seconds. And the output of hwinfo --monitor --short is appended to monitor.log. This log file can give you the activity history of monitor plug-in and plug-out.
FYI: I am using a background (daemon) python script using the above command (and other similar ones) to detect if someone is doing some HW plug-ins and plug-outs with the systems in the computer lab. If so, I get appropriate notifications that someone plugged-out/in a monitor, mouse or keyboard in almost real-time!
More info about hwinfo command is here. Its man page is also a good source.
sudo get-edid didn't work for me. (EDIT: now works on another computer, Lubuntu 14.10; I'd blame BIOS differences but that's a random guess...)
Anyway under X, xrandr --verbose prints the EDID block. Here is a quick and dirty way to extract it and pass to parse-edid:
#!/bin/bash
xrandr --verbose | perl -ne '
if ((/EDID(_DATA)?:/.../:/) && !/:/) {
s/^\s+//;
chomp;
$hex .= $_;
} elsif ($hex) {
# Use "|strings" if you dont have read-edid package installed
# and just want to see (or grep) the human-readable parts.
open FH, "|parse-edid";
print FH pack("H*", $hex);
$hex = "";
}'
If you don't want to parse xrandr output, write a C program using libXrandr that gets only what you want. If all you want to do is to query information, it can be done quickly. Read this document.
If you want to get the real monitor name, an alternative to #dtmilano's solution is to get the EDID property of the monitor using libXrandr and then manually parse it and print (read the EDID specification).
xrandr source code.
I know this is a dirty way, but it gives me some monitor model name even better than sudo get-edid|parse-edid. It reads information in arrays, and outputs it in a way that can be read like you would read a file. You may modify it according to your needs.
#!/bin/bash
#
#
# get-monitors.sh
#
# Get monitor name and some other properties of connected monitors
# by investigating the output of xrandr command and EDID data
# provided by it.
#
# Copyright (C) 2015,2016 Jarno Suni <8#iki.fi>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. See <http://www.gnu.org/licenses/gpl.html>
set -o nounset
set -o errexit
# EDID format:
# http://en.wikipedia.org/wiki/Extended_Display_Identification_Data#EDID_1.3_data_format
# http://read.pudn.com/downloads110/ebook/456020/E-EDID%20Standard.pdf
declare -r us=';' # separator string;
# If EDID has more than one field with same tag, concatenate them,
# but add this string in between.
declare -r fs=$'\x1f' # Field separator for internal use;
# must be a character that does not occur in data fields.
declare -r invalid_edid_tag='--bad EDID--'
# If base EDID is invalid, don't try to extract information from it,
# but assign this string to the fields.
# Get information in these arrays:
declare -a outs # Output names
declare -a conns # Connection type names (if available)
declare -a names # Monitor names (but empty for some laptop displays)
declare -a datas # Extra data; may include laptop display brand name
# and model name
declare -i no # number of connected outputs (to be counted)
# xrandr command to use as a source of information:
declare -r xrandr_output_cmd="xrandr --prop"
hex_to_ascii() {
echo -n "$1" | xxd -r -p
}
ascii_to_hex() {
echo -n "$1" | xxd -p
}
get_info() {
no=0
declare OIFS=$IFS;
IFS=$fs
while read -r output conn hexn hexd; do
outs[no]="${output}"
conns[no]="${conn}"
names[no]="$(hex_to_ascii "$hexn")"
datas[no]="$(hex_to_ascii "$hexd")"
(( ++no ))
done < <(eval $xrandr_output_cmd | gawk -v gfs="$fs" '
function print_fields() {
print output, conn, hexn, hexd
conn=""; hexn=""; hexd=""
}
function append_hex_field(src_hex,position,app_hex, n) {
n=substr(src_hex,position+10,26)
sub(/0a.*/, "", n)
# EDID specification says field ends by 0x0a
# (\n), if it is shorter than 13 bytes.
#sub(/(20)+$/, "", n)
# strip whitespace at the end of ascii string
if (n && app_hex) return app_hex sp n
else return app_hex n
}
function get_hex_edid( hex) {
getline
while (/^[ \t]*[[:xdigit:]]+$/) {
sub(/[ \t]*/, "")
hex = hex $0
getline
}
return hex
}
function valid_edid(hex, a, sum) {
if (length(hex)<256) return 0
for ( a=1; a<=256; a+=2 ) {
# this requires gawk
sum+=strtonum("0x" substr(hex,a,2))
# this requires --non-decimal-data for gawk:
#sum+=sprintf("%d", "0x" substr(hex,a,2))
}
if (sum % 256) return 0
return 1
}
BEGIN {
OFS=gfs
}
/[^[:blank:]]+ connected/ {
if (unprinted) print_fields()
unprinted=1
output=$1
}
/[^[:blank:]]+ disconnected/ {
if (unprinted) print_fields()
unprinted=0
}
/^[[:blank:]]*EDID.*:/ {
hex=get_hex_edid()
if (valid_edid(hex)) {
for ( c=109; c<=217; c+=36 ) {
switch (substr(hex,c,10)) {
case "000000fc00" :
hexn=append_hex_field(hex,c,hexn)
break
case "000000fe00" :
hexd=append_hex_field(hex,c,hexd)
break
}
}
} else {
# set special value to denote invalid EDID
hexn=iet; hexd=iet
}
}
/ConnectorType:/ {
conn=$2
}
END {
if (unprinted) print_fields()
}' sp=$(ascii_to_hex $us) iet=$(ascii_to_hex $invalid_edid_tag))
IFS="$OIFS"
}
get_info
# print the colums of each display quoted in one row
for (( i=0; i<$no; i++ )); do
echo "'${outs[i]}' '${conns[i]}' '${names[i]}' '${datas[i]}'"
done
You may try ddcprobe and/or get-edid
$ sudo apt-get install xresprobe read-edid
$ sudo ddcprobe
$ sudo get-edid
You're looking for EDID information, which is passed along an I²C bus and interpreted by your video driver. As dtmilano says, get-edit from ddcprobe should work.
You can also get this information by logging your X start:
startx -- -logverbose 6
Years ago, I used a package called read-edid to gather this information.
The read-edid package may be available in Ubuntu already, according to this blog post from 2009.