technikhaufen - debian

dd can not count

nospam@example.com (Michael Gebetsroither) — Sun, 15 Jun 2008 18:36:43 +0200

How much is 5*1kB?

128Byte as of dd.

% strace -e read,open dd if=/dev/random of=foo bs=1k count=5

open("/dev/random", O_RDONLY|O_LARGEFILE) = 0
read(0, "\347P\203\355\206O;\362f\263v{s\327\206\354\302{\21\5\203"..., 1024) = 96
read(0, "U\16ee\330\304\264@", 1024)    = 8
read(0, "\316\26\363\\\26j\377\10", 1024) = 8
read(0, "K\331.\273,\200\4\234", 1024)  = 8 
read(0, "\2312\323/\304\376\n\261", 1024) = 8
0+5 records in
0+5 records out
128 bytes (128 B) copied, 2.85809 seconds, 0.0 kB/s

Seems 128bytes are quite less than the requested 5kB.

% man 2 read

RETURN VALUE
On success, the number of bytes read is returned (zero indicates end of
file), and the file position is advanced  by this  number. It is not an
error if this number is smaller than the number  of  bytes  requested; ...

dd_rescue to the rescue

% dd_rescue -m 1k /dev/random foo

Summary for /dev/random -> foo:
dd_rescue: (info): ipos:         1.0k, opos:         1.0k, xferd:         1.0k
                   errs:      0, errxfer:         0.0k, succxfer:         1.0k
             +curr.rate:        0kB/s, avg.rate:        0kB/s, avg.load:  0.0%

% ls -la foo

-rw-r----- 1 einstein einstein 1024 2008-06-15 18:35 foo

At lest dd_rescue is able to count correct.

Installing chrooted scponly on debian64

nospam@example.com (Michael Gebetsroither) — Thu, 01 May 2008 22:41:20 +0200

Install

apt-get update
apt-get install scponly

Configure

Reconfigure scponly to do chrooting.

dpkg-reconfigure scponly

Setup chroot

Debian has a script to help you with this task, but it's not without problems.

cd /usr/share/doc/scponly/setup_chroot
gunzip setup_chroot.sh.gz
sh setup_chroot.sh
> maybe use in/ instead of incoming/ ;)

Fixing chroot made by the script

And there are the problems:

The chroot is not working
Chroot is not updated as setup_chroot.sh just use cp

The first is not that hard to fix:

cp /lib64/ld-linux-x86-64.so.2 /home/scponly/lib
ln -s lib /home/scponly/lib64
mkdir /home/scponly/dev
cp -a /dev/null /home/scponly/dev

Fix for Winscp and some other clients

Compile this small programm to groups and copy it to /home/scponly/bin.

#include <string.h>
main()
{
        const char out[] = "root users\n";
        write(1, out, strlen(out));
        return 0;
}

diet gcc -O2 -s groups.c -o groups
cp groups /home/scponly/bin

Done

There is now a fully working chrooted scponly environment.
To upload something:

scp <FILE> scponly@<HOST>:in/

In my next post i'll descibe a possible solution for a chroot setup without any hassels and need to keep it in sync with the host-system.

Installing gitosis on debian

nospam@example.com (Michael Gebetsroither) — Mon, 31 Mar 2008 20:09:18 +0200

ATTENTION:

current gitosis debian package does a chmod -R git:git /var/cache/git, if you allready have a git repository setup be c arefully! #473574

Install

apt-get update
apt-get install gitosis

This creates a user git with /var/cache/git as $HOME (which is also the default directory for git-daemon to serve). I've changed this to the normal /home/git as i want gitosis only for non-public projects.

Initialise

% su git
$ gitosis-init </tmp/id_rsa.pub 
Initialized empty Git repository in ./
Initialized empty Git repository in ./

Configure

% git clone git@localhost:gitosis-admin.git
% cd gitosis-admin

see gitosis documentation if you need further help on configuration or http://scie.nti.st/2007/11/14/hosting-git-repositories-the-easy-and-secure-way

Problems:

ssh git@localhost:
```
Mar 31 14:27:06 god sshd[27051]: User git not allowed because account is locked
```
If you encounter something like this then you should update your adduser packet because it is broken. #433639
Fix: change the ! in /etc/shadow in the line of your git user to *.
gitosis config is not updated after push:
```
chmod 755 $(readlink ~git/repositories/gitosis-admin.git/hooks/post-update)
```
The post-update hook is not executable and is a link on debian (#473613), the above should temporarily fix this.