Increasing max files or folders per directory on Linux EXT filesystem

Posted on by Randy

If a (poorly coded) app reaches the maximum number of files or folders per directory in Linux, you may see errors like this:

Error happened when generating Download Link.
Please try again or Contact administrator.
(ERROR:mkdir)

A quick and dirty way to increase the limit (and overall performance of the system) is to add the dir_index flag to the ext filesystem, then reindex:

tune2fs -O dir_index /dev/sda3
updatedb &

AS Number Stats on Linux

Posted on by Randy

I’ve got a couple of Linux machines that are sitting outside of the Sflow ‘zone’ and AS traffic stats go unmeasured. I wanted to get a rough idea on the number of connections per AS number so here’s a little app that parses netstat and sorts AS numbers by number of connection.

NOTE1: This won’t work on Cpanel servers due to tmp restrictions.

NOTE2: Specify an alternative (e.g newer) GeoIPASNum.dat file with the –geo option.

wget http://djlab.com/stuff/asnum
chmod +x asnum
./asnum

Example output:

[root@mx1 ~]# ./asnum
(18) | RFC1918 or BOGON
(11) | AS29889 Fast Serv Networks, LLC
(4) | AS3320 Deutsche Telekom AG
(2) | AS7922 Comcast Cable Communications, Inc.

Quick and (very) dirty cron script

#!/bin.sh
#/root/doasnum.sh
#*/5 * * * * /root/./doasnum.sh >> /var/log/asnum.log

thedate=`date`
echo "***********************"
echo $thedate
/root/asnum
echo "***********************"

Don’t forget to rotate the logs.

#/etc/logrotate.d/asnum
/var/log/asnum.log
{
        rotate 7
        daily
        missingok
}

Clone a live linux system with Rsync over SSH

Posted on by Randy

Update: 5/3/17 — Add additional notes for CentOS7 (dracut + grub2) and XenServer targets

All commands are run on new server.

1. Boot into rescue mode (iso, pxe, ect).

2. Create partitions with ‘fdisk /dev/sda’. Type 83 for non-RAID fs, 82 for swap, type fd in the case of RAID (all partitions). Flag boot partition as bootable.

In the case of SSD, add -S 32 -H 32 to the fdisk command and start the first partition on sector 2 for proper alignment.

If using RAID, duplicate the partition table after creating it on the first disk:

dd if=/dev/sda of=/dev/sdb bs=1 count=64 skip=446 seek=446

2. Create RAID array (if applicable).

# For SSD, add: --chunk=128
mdadm --create /dev/md0 -e 0.90 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1  ## /boot
mdadm --create /dev/md1 -e 0.90 --level=1 --raid-devices=2 /dev/sda2 /dev/sdb2  ## Swap
mdadm --create /dev/md2 -e 0.90 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb3  ## /

3. Create filesystems

For spin disk:

mkfs.ext4 /dev/md0 # /dev/sda1 for non-RAID
mkfs.ext4 /dev/md2 # /dev/sda3 for non-RAID

For SSD (non RAID):

mkfs.ext4 -b 1024 -E stride=128,stripe-width=128 -O ^has_journal /dev/sda1
mkfs.ext4 -b 1024 -E stride=128,stripe-width=128 -O ^has_journal /dev/sda3

For SSD (RAID):

mkfs.ext4 -b 1024 -E stride=128,stripe-width=256 -O ^has_journal /dev/md0 ## stripe-width = stride x N disks
mkfs.ext4 -b 1024 -E stride=128,stripe-width=256 -O ^has_journal /dev/md2 ## stripe-width = stride x N disks

4. Mount filesystems

mkdir /mount
mount /dev/md2 /mount  ## /dev/sda3 for non-RAID
mkdir {/mount/boot,/mount/dev,/mount/sys,/mount/proc,/mount/tmp}  
mount /dev/md0 /mount/boot ## /dev/sda1 for non-RAID

5. Sync filesystems with Rsync over SSH (Ex: 1.2.3.4 is source machine)

rsync -aHxv --numeric-ids --progress root@1.2.3.4:/* /mount --exclude=/dev --exclude=/proc --exclude=/sys --exclude=/tmp
rsync -aHxv --numeric-ids --progress root@1.2.3.4:/boot/* /mount/boot --exclude=/dev --exclude=/proc --exclude=/sys --exclude=/tmp  ## Only if /boot is on separate partition in source machine

If applicable: stop mysql on the source machine and resync the databases to prevent corruption:

rsync -aHxv root@1.2.3.4:/var/lib/mysql/* /mount/var/lib/mysql

6. Update mdadm.conf

mdadm --examine --scan > /mount/etc/mdadm.conf

7. Update fstab (if needed)

ls -la /dev/disk/by-uuid # to get new UUID's
vi /mount/etc/fstab

8a. Install bootloader (CentOS5, CentOS6 / grub)

grub
root (hd0,0)
setup (hd0)
root (hd1,0)  ## for RAID
setup (hd1)  ## for RAID
exit

8b. Install bootloader (CentOS7 / grub2)

Do step 10 (chroot) first, then this

grub2-install /dev/sda # Use correct device(s), repeat as neccesary
# Good time to clean up /etc/default/grub, then:
grub2-mkconfig -o /etc/grub2.cfg

# If migrating to Xen/XenServer:
dracut --add-drivers "xen-blkfront xen-netfront xen:vbd" --regenerate-all --force

9. Optional: change IP address if both machines need to be online

vi /mount/etc/sysconfig/network-scripts/ifcfg-eth0

10. Hint: you can chroot into the cloned filesystem – for example – initramfs rebuilding:

cd /mount/
mount -t proc proc proc/
mount -t sysfs sys sys/
mount -o bind /dev dev/
chroot .

11. Cross fingers, reboot

reboot

Find symlinks on Cpanel

Posted on by Randy

Find all possible root symlinks (leftover from attempted exploits) and save them as a list ‘symlinks.txt’.

ls /var/cpanel/users | grep -v "\`\|\.\|cpanel\|root\|mysql\|nobody" | \
while read CPUSER; do find /home/$CPUSER -type l -not \( -lname "/home/$CPUSER/*" \
-o -lname "*rvsitebuilder*" -o -lname "[^/]*" -o -lname "/usr/local/apache/domlogs/*" \
-o -lname "/usr/local/urchin/*" \) ; done \
> symlinks.txt &

Simple Monitoring with Email Alerts that works on LSI MegaRAID and Adaptec

Posted on by Randy

This tool will poll the output of command(s) or URL(s), and send email alerts if the output changes, contains (or not contains) certain text, or becomes unavailable. It’s a light weight, reliable monitoring replacement for the pile of garbage most RAID vendors include with their cards. Complex excludes and finds can be specified as Perl regex patterns — useful for suppression various noise (RAID verify, ect). The default configuration includes examples that will monitor local LSI or Adaptec cards.

Note – Tested on CentOS only. if someone wants to try Alien on Debian please let me know how it works.

rpm -ivh http://djlab.com/stuff/cloud-mon-1.1-3.i686.rpm

After installation, edit /etc/cloud.ini then:

service cloud-mon restart

Make sure you have logrotate installed to prevent log growth. This package includes a simple logrotate script.