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2026-06-26T10:46:21Z
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Kenneth: /* Set Random hostid */
2017-07-12T00:20:40Z
<p><span dir="auto"><span class="autocomment">Set Random hostid</span></span></p>
<p><b>New page</b></p><div>== Test Set Hostid ==<br />
<br />
<pre><br />
#include <stdio.h><br />
#include <unistd.h><br />
<br />
int main() {<br />
long id,res;<br />
<br />
// get real (default) hostid<br />
id = gethostid();<br />
printf("current hostid is: %xq\n",id);<br />
// set new hostid if is superuser<br />
res = sethostid(0x11223344);<br />
if (res == 0) printf("if result is zero - success! (%d) \n",res);<br />
// check if it is changed....<br />
id = gethostid();<br />
printf("current hostid is: %x ;-PPPppppp\n",id);<br />
}<br />
</pre><br />
<br />
Source: http://www.edaboard.com/thread5989.html<br />
<br />
== Example ==<br />
<br />
Host ID is stored in /etc/hostid as 4 bytes in reverse byte order<br />
<br />
<pre><br />
# hostid<br />
11223344<br />
<br />
# xxd /etc/hostid<br />
0000000: 4433 2211 D3".<br />
</pre><br />
<br />
=== Set Hostid ===<br />
<br />
To print a byte, you need to convert it to octal first:<br />
i=65 # ASCII 'A'<br />
printf \\$(printf "%o" $i); # 'A'<br />
<br />
<pre><br />
HOSTID=11223344<br />
<br />
C1=`echo $HOSTID | cut -b 7-8`<br />
C2=`echo $HOSTID | cut -b 5-6`<br />
C3=`echo $HOSTID | cut -b 3-4`<br />
C4=`echo $HOSTID | cut -b 1-2`<br />
<br />
# Convert to Decimal<br />
C1=`printf "%d" 0x$C1`<br />
C2=`printf "%d" 0x$C2`<br />
C3=`printf "%d" 0x$C3`<br />
C4=`printf "%d" 0x$C4`<br />
<br />
# Covert to Octal<br />
C1=`printf "%03o" $C1`<br />
C2=`printf "%03o" $C2`<br />
C3=`printf "%03o" $C3`<br />
C4=`printf "%03o" $C4`<br />
<br />
# Convert to Byte<br />
C1=`printf \\\\$C1`<br />
C2=`printf \\\\$C2`<br />
C3=`printf \\\\$C3`<br />
C4=`printf \\\\$C4`<br />
<br />
# Export to /etc/hostid<br />
printf "$C1$C2$C3$C4" > /etc/hostid<br />
<br />
# Test<br />
hostid<br />
</pre><br />
<br />
=== Set Random hostid ===<br />
<br />
sethostid<br />
<pre><br />
#!/bin/bash<br />
<br />
if [ "$1" != "" ] ; then<br />
<br />
HOSTID=$1<br />
<br />
# Check length<br />
CC=`echo $HOSTID | wc -c`<br />
if [ $CC -lt 8 ] ; then<br />
echo "Set random hostid or specify [AABBCCDD]"<br />
echo "Usage: $0 [AABBCCDD]"<br />
exit 1<br />
fi<br />
<br />
# Get first 4 hex bytes<br />
C1=`echo $HOSTID | cut -b 7-8`<br />
C2=`echo $HOSTID | cut -b 5-6`<br />
C3=`echo $HOSTID | cut -b 3-4`<br />
C4=`echo $HOSTID | cut -b 1-2`<br />
<br />
#printf "Setting hostid: $C4$C3$C2$C1\n"<br />
<br />
# Convert to Decimal<br />
C1=`printf "%d" 0x$C1`<br />
C2=`printf "%d" 0x$C2`<br />
C3=`printf "%d" 0x$C3`<br />
C4=`printf "%d" 0x$C4`<br />
<br />
else<br />
<br />
# Generate random hostid<br />
C1=$(( $RANDOM % 256 ))<br />
C2=$(( $RANDOM % 256 ))<br />
C3=$(( $RANDOM % 256 ))<br />
C4=$(( $RANDOM % 256 ))<br />
<br />
# Show Hex<br />
#printf "Setting hostid: %x%x%x%x \n" $C4 $C3 $C2 $C1<br />
<br />
fi<br />
<br />
# Covert to Octal<br />
C1=`printf "%03o" $C1`<br />
C2=`printf "%03o" $C2`<br />
C3=`printf "%03o" $C3`<br />
C4=`printf "%03o" $C4`<br />
<br />
# Convert to Byte<br />
C1=`printf \\\\$C1`<br />
C2=`printf \\\\$C2`<br />
C3=`printf \\\\$C3`<br />
C4=`printf \\\\$C4`<br />
<br />
# Export to /etc/hostid<br />
printf "$C1$C2$C3$C4" > /etc/hostid<br />
<br />
# Test<br />
hostid<br />
</pre></div>
Kenneth