[CentOS] Modify Parameters at system boot

JB jb.1234abcd at gmail.com
Fri May 13 12:28:10 UTC 2011


Frederick Abrams <fred at ...> writes:

> ... 

***
Look at /etc/rc.sysinit, by which time proc is already mounted:

...
# Configure kernel parameters
update_boot_stage RCkernelparam
<================= insert debugging statements BEFORE sysctl
sysctl -e -p /etc/sysctl.conf >/dev/null 2>&1
for file in /etc/sysctl.d/* ; do
        is_ignored_file "$file" && continue
        test -f "$file" && sysctl -e -p "$file" >/dev/null 2>&1
done
<================= insert debugging statements AFTER sysctl

You can modify this script and add debugging statements before and after this
code (marked <===== ), like:

echo "debugging BEFORE sysctl" >> /test.out
ls -l /proc/sys/net/ipv4/netfilter/ip_conntrack_max >> /test.out 2>&1
echo "/proc/sys/net/ipv4/netfilter/ip_conntrack_max=" >> /test.out
cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max >> /test.out 2>&1

and repectively

echo "debugging AFTER sysctl" >> /test.out
ls -l /proc/sys/net/ipv4/netfilter/ip_conntrack_max >> /test.out 2>&1
echo "/proc/sys/net/ipv4/netfilter/ip_conntrack_max=" >> /test.out
cat /proc/sys/net/ipv4/netfilter/ip_conntrack_max >> /test.out 2>&1

***
Also, remember that:
- sysctl can load from any other file than sysctl.conf during boot time
- 'sysctl -w' can write to and modify proc 
- echo "..." > /proc/... style entries can do the same from anywhere

So, it may be prudent to scan for these entries in:
grep -ir sysctl /etc/rc*
grep -ir sysctl /etc/init*
grep -ir sysctl /etc/sysconfig
grep -ir sysctl /root/

or, just to pick one of your cases:

grep -ir net.ipv4.netfilter.ip_conntrack_max /etc
grep -ir net.ipv4.netfilter.ip_conntrack_max /root

***
Last thing to consider.
Note that in that script snippet above there is this line

...
update_boot_stage RCkernelparam
...

The function update_boot_stage deals with Plymouth.
RHGB stands for RedHat Grapical Boot.
You can try to remove it (and "quiet" too for a good measure) from Grub kernel
boot line, by pressing the 'a' key at Grub startup and editing the kernel
command line.

Btw, any funny Grub kernel boot parameters beyond that ?

JB





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