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Felix J. Ogris' private homepage: some stuff about homemade software, FreeBSD, Linux, computers, and hacking in general.

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recent news

[2023-11-25] formdata.py shows how to do multipart/form-data HTTP POST uploads with Python's urllib only.

[2023-11-05] Benchmarked two additional devices for video encoding speed.

[2023-09-16] I benchmarked my graphic cards for video encoding speed and kept the results as my personal reference.

[2023-09-15]

New version of privatebinc.py, which is a simple Python client for PrivateBin, now allows you to specify a password, which the user has to enter in order to view the text and maybe the attached file. In addition, it fixes the bug where I forgot to base64 encode the attachment 🤦
How to use Apache Tomcat and TLS/SSL certificates in PEM or PKCS12 format.

[2023-09-13]

Updated initramfs for LVM runs fsck (just for ext2, ext3, and ext4) if you add dofsck to the kernel command line, and shows how to create an LVM snapshot of your root filesystem if you add dosnap to the kernel command line.
Corollary of yesterday's SQLite ramblings: The following command initialises the database and the counter table, but does not modify them if the event counter has already been used. Thus, you may execute these statements several times without corrupting any data:
```
$ sqlite3 /tmp/counter.sqlite "CREATE TABLE IF NOT EXISTS counter (id INT NOT NULL PRIMARY KEY); INSERT INTO counter SELECT 0 WHERE (SELECT COUNT(*) FROM counter)=0;"
```

[2023-09-12] The other day I needed an event counter shared between scripts written in Python and Perl. These scripts process incoming files at a very low rate, about 10 per hour. Their filenames should be prefixed with an increasing and unique id. A text file containing the next id, protected by a file lock, is complicated, error-prone, and most likely non-portable. Same counts for a shared memory segment, plus this is lost at a reboot. A full blown SQL server seemed to be overkill. Thus, SQLite came to my mind. It has been part of Python since version 2.5, and is available, if not even installed, on many operating systems. The scripts are quite trivial. For Python:

#!/usr/bin/python

import sqlite3

con = sqlite3.connect("/tmp/counter.sqlite", isolation_level=None)
cur = con.cursor()
(next_id,) = cur.execute("UPDATE counter SET id=id+1 RETURNING id").fetchone()
con.close()
print(next_id)

Perl counterpart:

#!/usr/bin/perl -w

use strict;
use warnings;
use DBI;

my $dbh = DBI->connect("DBI:SQLite:dbname=/tmp/counter.sqlite", "", "", {
  AutoCommit => 1, RaiseError => 1
});
my ($next_id) = $dbh->selectrow_array("UPDATE counter SET id=id+1 RETURNING id");
$dbh->disconnect();
print "$next_id\n";

Of course you have to initialise the database and the counter table upfront, e.g. by using the sqlite3 command line tool:

$ sqlite3 /tmp/counter.sqlite "CREATE TABLE counter (id INT NOT NULL PRIMARY KEY); INSERT INTO counter VALUES (0);"

A bonus variant written in C:

/* Compile with:
 * cc -W -Wall -O3 -pipe -s -o counter counter.c -lsqlite3
 */
#include <stdio.h>
#include <err.h>
#include <sqlite3.h>

int main ()
{
  const char sql[] = "UPDATE counter SET id=id+1 RETURNING id";
  sqlite3 *db;
  sqlite3_stmt *stmt;
  int next_id;

  if (sqlite3_open("/tmp/counter.sqlite", &db) != SQLITE_OK)
    errx(1, "sqlite3_open: %s",
         db ? sqlite3_errmsg(db) : "Generic SQLite error");

  if (sqlite3_prepare_v2(db, sql, sizeof(sql), &stmt, NULL) != SQLITE_OK)
    errx(1, "sqlite3_prepare_v2: %s", sqlite3_errmsg(db));

  if (sqlite3_step(stmt) != SQLITE_ROW)
    errx(1, "sqlite3_step: %s", sqlite3_errmsg(db));

  next_id = sqlite3_column_int(stmt, 0);

  if (sqlite3_finalize(stmt) != SQLITE_OK)
    errx(1, "sqlite3_finalize: %s", sqlite3_errmsg(db));

  if (sqlite3_close_v2(db) != SQLITE_OK)
    errx(1, "sqlite3_close_v2: %s", sqlite3_errmsg(db));

  printf("%i\n", next_id);

  return 0;
}

[2023-09-09]

double.pl, which finds duplicate files, updated after more than 17 years. I remember this being one of the very first Perl scripts I wrote on Linux. Thus, it must be 22 or so years old. Anyhow, it has been tidied, does not need any external programs, and uses just standard Perl modules.
rrdquery.pl version 5 just comes with correct examples.
pgnumeric.c shows how to store values of type numeric in a PostgreSQL database using C datatypes.
rtgen.py generates blackhole routes suitable for stress testing the Bird Internet Routing Daemon and other network gear, e.g. your BGP routers.
spf.pl shows how to use Perl's Mail::SPF module.
bsdrss prints the state and RSS of a process on DragonFlyBSD, FreeBSD, NetBSD, and OpenBSD.
regexplode.pl shows what happens if you accept arbitrary regular expressions, while regexplode.py shows why you want to use RE2 or pyre2.

[2023-09-08]

HTML files and folder symbols
mce.py is just a Python CGI script to play around with TinyMCE.
argparser.py shows how to use Python's argparse module.
smtp.py shows how to send quoted-printable encoded emails containing UTF-8 characters in both the subject and the body using Python's smtplib and email.message modules.
s3.php shows how to use the AWS SDK for PHP with an S3 object storage.
Kernel-System-LinkObject.pm.diff is a patch for the LinkObject module of OTRS and Znuny. If have several thousand linked tickets and your system becomes sluggish, try this patch.
nswl@.service shows how to run multiple instances of the NetScaler web server logging client on a recent Linux distribution as it comes as service unit for systemd.

[2023-09-04] How to show git log entries up to a certain date:

$ git --no-pager log -1 --until "2023-06-22"
$ git --no-pager log -1 --until "last year"

You can then use the commit hash from the above outputs for further processing, e.g.:

$ git diff --stat <commit hash>

[2023-08-23] How to get the current date and time of Lisbon:

Python:

import datetime, zoneinfo
print(datetime.datetime.now().astimezone(zoneinfo.ZoneInfo("Europe/Lisbon")).isoformat())

Perl:

{
  local $ENV{TZ} = "Europe/Lisbon";
  print scalar localtime();
}

bash, zsh, sh:
```
TZ="Europe/Lisbon" date
```

(t)csh:

setenv TZ "Europe/Lisbon"
date
unsetenv TZ

/*
 * compile with:
 * cc -W -Wall -O3 -s -pipe -o dtlisbon dtlisbon.c
 */

#include <stdlib.h>
#include <err.h>
#include <time.h>
#include <stdio.h>

int main ()
{
  char *oldtz, datetime[64];
  time_t now = time(NULL);

  oldtz = getenv("Europe/Lisbon");
  if (setenv("TZ", "Europe/Lisbon", 1))
    err(1, "setenv");

  strftime(datetime, sizeof(datetime), "%F %T %Z", localtime(&now));
  puts(datetime);

  if (oldtz && setenv("TZ", oldtz, 1))
    err(1, "setenv");

  return 0;
}

PostgreSQL:

SELECT now() at time zone 'Europe/Lisbon';

[2023-08-09] rrdquery.pl version 4 (obviously) comes with version numbering, an example section, and fixes two bugs, where a "IS NULL" predicate wasn't parsed correctly and an aggregate function was always expected.

[2023-08-03] dnskey2id.pl shows how to derive the key id for a given DNSSEC dnskey in Perl. Inspired by a Python snippet I found on https://lists.isc.org/pipermail/bind-users/2010-October/081724.html.

[2023-07-27] LogBlitz version 15 reduces the number and size of http cookies, and displays the number and size of the selected logfiles.

[2023-05-23] ampctrld version 2 lowers the number of addresses to listen on to a maximum of 16.

[2021-04-28]

New version of kvmlib comes with 5 new features:
- The cmd command, which connects you to the monitor of a running QEMU instance, now accepts additional parameters, which are passed to the monitor
- Previously, the detect-zeroes option for hard drives was set to unmap by default. As I encountered problems with virtual drives, regardless of the guest operating system, detect-zeroes is not set anymore
- Fixed the bug that prevented you from configuring up to 4 virtual cdrom drives
- You can close and eject any cdrom by specifing its drive number (0-3)
- Improved help
The CARP (Common Address Redundancy Protocol) of the upcoming FreeBSD 14 has two major changes:
1. By using the peer or peer6 parameter, carp uses unicast instead of multicast. This is helpful if your FreeBSD hosts run as virtual machines.
2. CARP creates no virtual network interface anymore. ifconfig carp0 create won't work. Instead, you assign it as an alias to the physical interface:
```
# ifconfig vtnet0 vhid 31 advskew 100 peer 192.168.0.29 pass foobar 192.168.0.31/24 alias
```
  Of course you have to load the carp module before: kldload carp. Then, ifconfig vtnet0 prints:
  
  To make this persistent after reboot, add it to /etc/rc.conf:
```
# sysrc kld_list+=carp
# sysrc ifconfig_vtnet0_alias0="vhid 31 advskew 100 peer 192.168.0.29 pass foobar 192.168.0.31/24"
```

[2021-04-25] New version of kvmlib allows you to use a different QEMU executable than qemu-system-x86_64, and exits with an error message if you use the cdrom command without a path to an ISO file.

[2023-04-23] If your recent Gentoo Linux box complains that /var/tmp already exists and is not a directory during system boot, i.e. maybe because it is a symlink to /tmp, then create a file named /etc/tmpfiles.d/tmp.conf containing this configuration:

L /var/tmp - - - - /tmp

For further details, you'll have to read the man page of systemd-tmpfiles.

[2023-04-17] If you run a Cyrus IMAP server that suddenly stops exporting some or even all calendar events, you might consider reconstructing the respective mailboxes, e.g. on a FreeBSD server:

# su - cyrus
% sbin/reconstruct -nrGR user.username.#calendars
% sbin/reconstruct -rGR user.username.#calendars

[2023-03-29] grapheqd version 7 supports IPv6 addresses and can listen on multiple addresses at the same time.

[2023-03-28] As announced 18 days ago, ampctrld is a re-implementation of ampcontrol in plain C. It has two new features: It allows you to assign user-defined names to input sources, and can listen on multiple addresses, i.e. an IPv4 and an IPv6 address at the same time. Additionally, it saves system resources:

And:

[2023-03-27] How to get the base64 encoded SHA hash of an existing file, part two:

C, using the OpenSSL API: sha512.c

[2023-03-10] New version of ampcontrol handles initial connection errors, and makes use of the new Buffer API of Node.js.
I need to rewrite it again, though. This time in C, since memory consumption of Node.js is far too heavyweight for my taste:

[2023-02-25]

grapheqd version 6 fixes a typo which threw an error if compiling for ALSA, i.e. on Linux.
LogBlitz version 14 allows you to adjust the logout button, e.g. add a JavaScript onclick handler.

[2023-02-16] LogBlitz version 13 allows you to assign user roles based on additional environment settings.

[2023-02-15] LogBlitz version 12 introduces user roles.

[2023-01-28] LogBlitz version 11 saves selected filenames in a cookie, and uses different cookies for each user.

[2022-12-18] How to get the base64 encoded SHA hash of an existing file:

Python:

import hashlib, base64
print(base64.b64encode(hashlib.sha512(open("/etc/passwd", "rb").read()).digest()))

Perl:

use Digest::SHA;
my $b64_sha512 = Digest::SHA->new("sha512")->addfile("/etc/passwd", "b")->b64digest;
print($b64_sha512, "=" x ((4 - length($b64_sha512) % 4) % 4));

Shell:

$ openssl sha512 -binary /etc/passwd | openssl base64 -A

[2022-12-09] LogBlitz version 10 comes with a performance improvement if you don't search for regular expressions.

[2022-12-04] My new howto Apache and form based login makes use of mod_auth_form.

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