Adding a User with Sudo Access using visudo

Use the command visudo to access the /etc/sudoers file.

visudo

Uncomment this line:

## Allows people in group wheel to run all commands
# %wheel        ALL=(ALL)       ALL

So it looks like:

## Allows people in group wheel to run all commands
 %wheel        ALL=(ALL)       ALL

Save the file then

Run this command for your user

usermod -aG wheel usernameforsudoaccesshere

Your done.

But test it

su usernamewithsudoaccess
sudo yum history

Any root only command is a good enough test for this. The command should run succesfully after re-providing your users password for sudo access.

Retrieving SMART status from a SDA disk attached to a MegaRAID card

Today I realised that manually checking the smart status of a disk required a bit more.

[[email protected] ~]# smartctl -a -d megaraid,0 /dev/sda
smartctl 5.43 2016-09-28 r4347 [x86_64-linux-2.6.32-696.16.1.el6.x86_64] (local build)
Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net

Vendor:               SEAGATE
Product:              ST3146356SS
Revision:             HS10
User Capacity:        146,815,733,760 bytes [146 GB]
Logical block size:   512 bytes
Logical Unit id:      -----
Serial number:        ----
Device type:          disk
Transport protocol:   SAS
Local Time is:        Thu Mar 15 05:18:57 2018 CDT
Device supports SMART and is Enabled
Temperature Warning Disabled or Not Supported
SMART Health Status: OK

Current Drive Temperature:     32 C
Drive Trip Temperature:        68 C
Elements in grown defect list: 15
Vendor (Seagate) cache information
  Blocks sent to initiator = 3694557980
  Blocks received from initiator = 4259977977
  Blocks read from cache and sent to initiator = 2859908284
  Number of read and write commands whose size <= segment size = 1099899109
  Number of read and write commands whose size > segment size = 0
Vendor (Seagate/Hitachi) factory information
  number of hours powered up = 65098.07
  number of minutes until next internal SMART test = 23

Error counter log:
           Errors Corrected by           Total   Correction     Gigabytes    Total
               ECC          rereads/    errors   algorithm      processed    uncorrected
           fast | delayed   rewrites  corrected  invocations   [10^9 bytes]  errors
read:   105645673        6         0  105645679   105645679      65781.538           0
write:         0        0        38        38         45      48511.618           7
verify: 48452245        7         0  48452252   48452259      43540.092           7

Non-medium error count:       48

SMART Self-test log
Num  Test              Status                 segment  LifeTime  LBA_first_err [SK ASC ASQ]
     Description                              number   (hours)
# 1  Background long   Completed                  16       1                 - [-   -    -]
# 2  Background short  Completed                  16       0                 - [-   -    -]

In order to retrieve this detail you need to use -d megaraid,n where n is the disk id number. Try 0, 1, 2, 3, etc. Or use the megaraidCLI to get a list of all the disks. I dunno I thought it was worth mentioning at least. It always pays to check this if customer is having weird I/O troubles. Quite a lot of detail is provided about errors the disk encounters. So looking here, even if SMART OK. Gives you an idea if any test failing for disk.

Converting a QEMU qcow2 cloud server image to an native disk img and putting on physical disk

Got this question at work a lot. Thought I’d finally get around to putting it down since it’s came up for me. I’ve got a virtual machine using virtio passthrough for my pcie, and I found actually that disk access via the qcow2 is pretty naff.

sudo apt-get install qemu-kvm

qemu-img convert windows10cloudimage.qcow2 -O raw diskimage.img

dd if=/path/to/windos10cloudimage.qcow2 of=/dev/sdc2

Please note in my case the physical partition I’d made was sdc2. I’d actually resized another 5TB disk I have in my system using gparted. Just so I can attach a physical partition with libvirtd. Evidently though libvirtd-manager doesn’t allow this business so I have to edit the xlm file in /etc/qemu/windows10.xml .

 

[email protected]:/etc/libvirt/qemu# virsh  define /etc/libvirt/qemu/win10-uefi.xml 
Domain win10-uefi defined from /etc/libvirt/qemu/win10-uefi.xml
[email protected]:/etc/libvirt/qemu# virt-manager

yeah baby!


You could alternatively do it all in one like below, though you may desire a copy of the img file as well as putting it to the disk.

qemu-img convert windows10.qcow2 -O raw /dev/sdc

Less Ghetto Log Parser for Website Hitcount/Downtime Analysis

Yesterday I created a proof of concept script, which basically goes off and identifies the hitcounts of a website, and can give a technician within a short duration of time (minutes instead of hours) exactly where hitcounts are coming from and where.

This is kind of a tradeoff, between a script that is automated, and one that is flexible.

The end goal is to provide a hitcount vs memory commit metric value. A NEW TYPE OF METRIC! HURRAH! (This is needed by the industry IMO).

And also would be nice to generate graphing and mean, average, and ranges, etc. So can provide output like ‘stat’ tool. Here is how I have progress

#!/bin/bash
#
# Author: 	Adam Bull, Cirrus Infrastructure, Rackspace LTD
# Date: 	March 20 2017
# Use:		This script automates the analysis of webserver logs hitcounts and
# 		provides a breakdown to indicate whether outages are caused by website visits
#		In correlation to memory and load avg figures


# Settings

# What logfile to get stats for
logfile="/var/log/httpd/google.com-access.log"

# What year month and day are we scanning for minute/hour hits
year=2017
month=Mar
day=9

echo "Total HITS: MARCH"
grep "/$month/$year" "$logfile" | wc -l;

# Hours
for i in 0{1..9} {10..24};

do echo "      > 9th March 2017, hits this $i hour";
grep "$day/$month/$year:$i" "$logfile" | wc -l;

        # break down the minutes in a nested visual way thats AWsome

# Minutes
for j in 0{1..9} {10..60};
do echo "                  >>hits at $i:$j";
grep "$day/$month/$year:$i:$j" "$logfile" | wc -l;
done

done

Thing is, after I wrote this, I wasn’t really happy, so I refactored it a bit more;

#!/bin/bash
#
# Author: 	Adam Bull, Cirrus Infrastructure, Rackspace LTD
# Date: 	March 20 2017
# Use:		This script automates the analysis of webserver logs hitcounts and
# 		provides a breakdown to indicate whether outages are caused by website visits
#		In correlation to memory and load avg figures


# Settings

# What logfile to get stats for
logfile="/var/log/httpd/someweb.biz-access.log"

# What year month and day are we scanning for minute/hour hits
year=2017
month=Mar
day=9

echo "Total HITS: $month"
grep "/$month/$year" "$logfile" | wc -l;

# Hours
for i in 0{1..9} {10..24};

do
hitsperhour=$(grep "$day/$month/$year:$i" "$logfile" | wc -l;);
echo "    > $day $month $year, hits this $ith hour: $hitsperhour"

        # break down the minutes in a nested visual way thats AWsome

# Minutes
for j in 0{1..9} {10..59};
do
hitsperminute=$(grep "$day/$month/$year:$i:$j" "$logfile" | wc -l);
echo "                  >>hits at $i:$j  $hitsperminute";
done

done

Now it’s pretty leet.. well, simple. but functional. Here is what the output of the more nicely refined script; I’m really satisfied with the tabulation.

[[email protected] automation]# ./list-visits.sh
Total HITS: Mar
6019301
    > 9 Mar 2017, hits this  hour: 28793
                  >>hits at 01:01  416
                  >>hits at 01:02  380
                  >>hits at 01:03  417
                  >>hits at 01:04  408
                  >>hits at 01:05  385
^C

Site keeps on going down because of spiders

So a Rackspace customer was consistently having an issue with their site going down, even after the number of workers were increased. It looked like in this customers case they were being hit really hard by yahoo slurp, google bot, a href bot, and many many others.

So I checked the hour the customer was affected, and found that over that hour just yahoo slurp and google bot accounted for 415 of the requests. This made up like 25% of all the requests to the site so it was certainly a possibility the max workers were being reached due to spikes in traffic from bots, in parallel with potential spikes in usual visitors.

[[email protected] logs]#  grep '01/Mar/2017:10:' access_log | egrep -i 'www.google.com/bot.html|http://help.yahoo.com/help/us/ysearch/slurp' |  wc -l
415

It wasn’t a complete theory, but was the best with all the available information I had, since everything else had been checked. The only thing that remains is the number of retransmits for that machine. All in all it was a victory, and this was so awesome, I’m now thinking of making a tool that will do this in more automated way.

I don’t know if this is the best way to find google bot and yahoo bot spiders, but it seems like a good method to start.

A Unique Situation for grep (finding the files with content matching a specific pattern Linux)

This article explains how to find all the files that have a specific text or pattern within them, this is the article you’ve been looking for!

So today, I was dealing with a customers server where he had tried to configure BASIC AUTH. I’d found the httpd.conf file for the specific site, but I couldn’t see which file had basic auth setup as wrong. To save me looking through hundreds of configurations (and also to save YOU from looking through hundreds of configuration files) for this specific pattern. Why not use grep to recursively search files for the pattern, and why not use -n to give the filename and line number of files which have text in that match this pattern.

I really enjoyed this oneliner, and been meaning to work to put something like this together, because this kind of issue comes up a lot, and this can save a lot of time!

 grep -rnw '/' -e "PermitRootLogin"

# OUTPUT looks like

/usr/share/vim/vim74/syntax/sshdconfig.vim:157:syn keyword sshdconfigKeyword PermitRootLogin
/usr/share/doc/openssh-5.3p1/README.platform:37:instead the PermitRootLogin setting in sshd_config is used.

The above searches recursively all files in the root filesystem ‘/’ looking for PermitRootLogin.

I wanted to find which .htaccess file was responsible so I ran;

# grep -rnw '/' -e "/path/to/.htpasswd'

# OUTPUT looks like
/var/www/vhosts/somesite.com/.htaccess:14:AuthUserFile /path/to/.htpasswd

Using omconfig to add a RAID 1 device for a Perc 6/i Dell Raid Controller

So, I’ve been provisioning disks, and stuff recently.. this is how I did it on a Dell. Quite an easy thing to do!

omconfig storage controller action=createvdisk controller=0 raid=r1 size=max readpolicy=ara pdisk=0:0:2,0:0:3
Command successful!

In this case the two disks newly added were 0:0:2 and 0:0:3 on the SAS ‘bus’.

An additional primary partition was created and added for this device sdb1, and a filesystem of the same kind (ext3) as the system disk was created;

 mkfs.ext3 /dev/sdb1

mke2fs 1.39 (29-May-2006)
....
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

You will naturally need to mount the partition and create an fstab entry to make this permanent;

mount /dev/sdb1 /mnt/backup

echo "/dev/sdb1               /mnt/backup             ext3    defaults        1 1" >> /etc/fstab

You may wish to consider adding the above to fstab manually. It’s not a good idea using echo with it incase you make a mistake ;-D

Cheers &
Best wishes,
Adam

Configuring SFTP without chroot (the easy way)

So, I wouldn’t normally recommend this to customers. However, there are secure ways to add SFTP access, without the SFTP subsystem having to be modified. It’s also possible to achieve similar setup in a location like /home/john/public_html.

Let’s assume that public_html and everything underneath it is chowned john:john. So john:john has all the access, and apache2 runs with it’s own gid;uid. This was a pretty strange setup, and you don’t see it every day. But actually, it allowed me to solve another problem that I’ve been seeing/seeing customers have for a long time. That problem is the problem of effectively and easily managing permissions. Once I figured this out it was a serious ‘aha!’ moment!. Here’s why.

Inside the /etc/group, we find the customers developer has done something tragic:

[[email protected] public_html]# cat /etc/group | grep apache
apache:x:48:john,bob

But fine.. we’ll run with it.

We can see all the files inside their /home/john/public_html , the sight is not good

]# ls -al 
total 232
drwxrwxr-x 27 john john  4096 Dec 20 15:56 .
drwxr-xr-x 12 john john  4096 Dec 15 11:08 ..
drwxrwxr-x 10 john john  4096 Dec 16 09:56 administrator
drwxrwxr-x  2 john john  4096 Dec 14 11:18 bin
drwxrwxr-x  4 john john  4096 Nov  2 15:05 build
-rw-rw-r--  1 john john   714 Nov  2 15:05 build.xml
drwxrwxr-x  3 john john  4096 Nov  2 15:05 c
drwxrwxr-x  3 john john 45056 Dec 20 13:09 cache
drwxrwxr-x  2 john john  4096 Dec 14 11:18 cli
drwxrwxr-x 32 john john  4096 Dec 14 11:18 components
-rw-rw-r--  1 john john  1863 Nov  2 15:05 configuration-live.php
-rw-r--r--  1 john john  3173 Dec 15 11:08 configuration.php
drwxrwxr-x  3 john john  4096 Nov  2 15:05 docs
drwxrwxr-x  8 john john  4096 Dec 16 17:17 .git
-rw-rw-r--  1 john john  1734 Dec 14 11:21 .gitignore

It gets worse..

# cat /etc/passwd | grep john
john:x:501:501::/home/john:/bin/sh

Now, adding an sftp user into this, might look like a nightmare, but actually with some retrospective thought it was really easy.

Solving this mess:

Install Scponly

yum install scponly

Create new ‘SFTP’ user:

scponlyuser:x:504:505::/home/john:/usr/bin/scponly

Create a password for user scponlyuser

 
passwd scponlyuser

Solution to john:john permissions

[[email protected] public_html]# cat /etc/group | grep john
apache:x:48:john,bob
john:x:501:scponlyuser

We simply make scponlyuser part of the john group by adding the second line there. That way, the scponlyuser will have read/write access to the same files as the shell user, without exposing any additional stuff.

This was a cool solution to fixing this customers insecure solution, that they wanted to keep it the way they had, and was also great way to add an sftp account without requiring root jail. Whether it’s better than the root jail, is really debatable, however scponly enforces that only this account can be used only for SCP, as well as achieving sftp user access, without a jail.

I was proud of this achievement.. goes to show Linux permissions are really more flexible than we can imagine. And, whether you really want to flex those permissions muscles though, should be of concern. I advised this customer to change this setup, remove the /bin/sh, among other things..

We finally test SFTP is working as expected with the new scponlyuser

sftp> rmdir test
sftp> get index.php
Fetching /home/john/public_html/index.php to index.php
/home/john/public_html/index.php                                                                                     100% 1420     1.4KB/s   00:00
sftp> put index.php
Uploading index.php to /home/john/public_html/index.php
index.php                                                                                                                100% 1420     1.4KB/s   00:00
sftp> mkdir test
sftp> rmdir test

Just replace ‘scponly’ with whatever username your setting up. The only part that you need to keep the ‘scponly’ bit, is /usr/bin/scponly, this is the environment logging into. Apologies that scponly is so similar to scponlyuser ;-D

scponlyuser:x:504:505::/home/john:/usr/bin/scponly

I was very pleased with this! Hope that you find this useful too!