Searching for cpu capabilities? Look at /proc/cpuinfo...

Most of us know, that with

cat /proc/cpuinfo

the number of cpus, cpu speed, cpu model etc. can be found. But there is one interesting line which is called flags:

processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.73GHz
stepping : 8
cpu MHz : 1733.000
cache size : 2048 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tm pbe bts est tm2
bogomips : 3457.11
clflush size : 64

Ok, the acronyms sound familiar. Here the outputs from some other cpus:

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr dca sse4_1 sse4_2 popcnt lahf_lm ida
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe constant_tsc pebs bts pni monitor ds_cpl cid xtpr

Hmmm. No flag like 64Bit or x64... How can this acronyms be decoded?
Let's ask the kernel sources!
There is one file inside the sources, where all this flags are defined:

arch/x86/include/asm/cpufeature.h

Here are the most interesting ones:

#define X86_FEATURE_HT (0*32+28) /* Hyper-Threading */
#define X86_FEATURE_LM (1*32+29) /* Long Mode (x86-64) */
#define X86_FEATURE_VMX (4*32+ 5) /* Hardware virtualization */
#define X86_FEATURE_PN (0*32+18) /* Processor serial number */

Just if you are not sure about installing 64Bit Linux, check for lm. And if ht is shown, you do not worry, can detect twice as much cores as there are, or if...

Batch processing: ssh access to multiple servers without ssh-keys

It is always the same: You are used to a technique like

• accessing server via ssh with ssh-keys

But in some environments you are not allowed or you just don't want to put your authorized_keys to the servers, which you want to access. But how to automate logins to this servers?

1. Poor man's approach
   buffer the password and use the middle button on your mouse, each time the script asks for the password.
   This works, but this is only "semi-automatic"
2. Use expect
   With this tool it is very easy to automate logins without using ssh-keys. Just write a script auto.ssh.sh like this:
   

#!/usr/bin/expect
spawn ssh -l root $argv
expect "Password: "
send "mypassword\n"
expect "#";
send "date\n";
expect "#";
send "exit\n";

This script can be called with a parameter (here IP or hostname) and executes the date command on the server. Now just write a loop:

for server in 10.0.0.1 10.0.0.2 10.0.0.3; do ./auto.ssh.sh $server; done

And you are done...
(But this is not so secure like using ssh-keys!)

Bash history for multiple shells...

Did you ever configure something and after a while you were not able to remember the exact syntax for the command?
If you used the bash shell, then the command history was your friend:

history|grep <part of command>

and you got everytime the line with the right command back.
Everytime? Hmm no. Sometimes the command did not show up in the history. First guess:

HISTFILESIZE

was not big enough, but there is another option for missing entries:
If you work with multiple shells at the same time, then the history will be (over)written by closing the last shell.
But this can be avoided:
After adding the following to your .bashrc, you will never miss an entry again ;-):

shopt -s histappend

For more information of shopt take a look here.

Linux: hash algorithms for passwords inside /etc/shadow

You read the headline and you are sure that this is easy to answer?
I was thinking the same: Just a MD5-hash inside this /etc/shadow file.

But this is not true anymore:
You can use several hash algorithms inside /etc/shadow like

• MD5
• blowfish
• DES
  
• SHA-256
• SHA-512
  

Inside /etc/shadow you can see the following:

schroff:$1$<String1>$<String2>:0:99999:7:::

$1$ stays for MD5, $2a$ for blowfish, $5$ for SHA-256, $6$ for SHA-512. The <String1> contains a salt and <String2> the hashed password.
The other values can be easily interpreted (and changed) with the following command:

schroff@hades:$ chage -l schroff
Letzte Passwortänderung : Feb 01, 2009
Passwort läuft ab : nie
Passwort inaktiv : nie
Benutzerzugang läuft ab : nie
Minimale Anzahl der Tage zwischen Passwortänderungen : 0
Maximale Anzahl der Tage zwischen Passwortänderungen : 99999
Anzahl Tage, an denen vor Passwortablauf gewarnt wird : 7

And where can the hash algorithm be changed? This depends on the linux you are using:

• /etc/pam.d/common-password (Debian)
• /etc/default/password (SUSE/Novell)

Is there a way to generate this passwords via command line? Yes, with debian package makepasswd (but only for MD5):

echo "mypasswd" | makepasswd --crypt-md5
$1$r2elYKyB$vUr/Ph.brKTldM2h2k8J5.

But this will not work via copy and paste inside /etc/shadow ;-(
To change password via script some linux distribution can use:

echo oracle:mypasswd | chpasswd

or

echo -n mypasswd | passwd --stdin oracle