Log file system changes using Audit

Adding an audit rule to log file-system activity:

# auditctl -w /home/something/ -p rwa

Flags:

-w Insert watch
-p Set the permission filter

If you search the audit log, you will only get results if there has been activity:

# ausearch -f /home/something/
<no matches>

Now, if we create a new file and search again:

# touch /home/something/testing1

# ausearch -f /home/something/
----
time->Tue Apr  9 08:53:08 2013
type=PATH msg=audit(1365511988.313:969510): item=1 name="/home/something/testing1" inode=54411 dev=08:15 mode=0100644 ouid=0 ogid=0 rdev=00:00 obj=user_u:object_r:user_home_t:s0
type=PATH msg=audit(1365511988.313:969510): item=0 name="/home/something/" inode=54374 dev=08:15 mode=040700 ouid=1041 ogid=1041 rdev=00:00 obj=user_u:object_r:user_home_dir_t:s0
type=CWD msg=audit(1365511988.313:969510):  cwd="/root"
type=SYSCALL msg=audit(1365511988.313:969510): arch=c000003e syscall=2 success=yes exit=0 a0=7fff217f4cb6 a1=941 a2=1b6 a3=32cc35410c items=2 ppid=10799 pid=26986 auid=1041 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=130958 comm="touch" exe="/bin/touch" subj=user_u:system_r:unconfined_t:s0 key=(null)

Let's delete the file and see what happens to the logs.

# rm /home/something/testing1

Run the search again:

# ausearch -f /home/something/

Notice the syscall key which is displayed in each entry.  What does the code mean?  Let's make things more 'readable' by setting the -i flag.

# ausearch -f /home/something/ -i
----
type=PATH msg=audit(04/09/2013 09:00:52.093:969611) : item=1 name=/home/something/testing1 inode=54411 dev=08:15 mode=file,644 ouid=root ogid=root rdev=00:00 obj=user_u:object_r:user_home_t:s0
type=PATH msg=audit(04/09/2013 09:00:52.093:969611) : item=0 name=/home/something/ inode=54374 dev=08:15 mode=dir,700 ouid=something ogid=something rdev=00:00 obj=user_u:object_r:user_home_dir_t:s0
type=CWD msg=audit(04/09/2013 09:00:52.093:969611) :  cwd=/root
type=SYSCALL msg=audit(04/09/2013 09:00:52.093:969611) : arch=x86_64 syscall=unlink success=yes exit=0 a0=7fff2c3b2cbc a1=1 a2=2 a3=168f7610 items=2 ppid=10799 pid=27302 auid=something uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=pts0 ses=130958 comm=rm exe=/bin/rm subj=user_u:system_r:unconfined_t:s0 key=(null) 

The timestamps are now all converted to human-readable formats.  The UIDs and GIDs are converted to the name of the user or group and finally, the system call codes show something intelligible.  For example, syscall=87 now reads syscall=unlink which which we can interpret as 'delete'.

You can search by system call codes as well.  Instead of displaying all activity on all files and reading through each entry one by one, you can search for 'unlink' system calls.

The flag is -sc <syscall>

For example, the following command will return the log(s) entry(ies) showing an 'unlink' call.

# ausearch -f /home/something/testing1 -i -sc unlink

To remove a watch, use the -W flag.  Note, when using this flag, the remove (-W) command must match the rule.  If you don't know the exact rule, you can list them:

# auditctl -l

LIST_RULES: exit,always dir=/home/something (0xe) perm=rwa

Now we can delete it using:

# auditctl -W /home/something -p rwa

Extending root partition on the fly - Part 2

In my previous post I discuss some techniques to expand disks while ensuring zero downtime.

These techniques are not always viable as it will depend on the Operating System version you have, as well as LVM version.  If you don't use LVM and instead use native linux partitions, then things can get a bit uglier and you will probably need one or two reboots.  In CentOS 5.2 I can't properly re-scan the ISCSI devices.  It seems support for it may have only been added in version 5.4, as RedHat began adding shell scripts to perform this operation.

In any case, for the latest version of RedHat and Centos (5.5,6,6.2,6.3) the previously described techniques work just fine.  There is only one caveat.  In order to prevent having to disable the volume group, unmounting the filesystem and stopping services that are using them, one must create a new "Physical Volume" using pvcreate, as I've done.  The only problem with this, and it's not a big one, is that you end up with separated physical volumes all on the same LVM partition.

If you want to expand the disk but have only one physical volume in the LVM, it will be necessary to disable the volume group in order to use pvresize.  Note that this implies shutting down services and unmounting the filesystem to be expanded.

Example:

1) Extend disk in vmware

2) Rescan the disk
# echo "1" > /sys/class/scsi_device/<device number>/device/rescan

3) resize the partition in question using fdisk <device>
# fdisk /dev/sdb

4) re-read the partition table:
# partprobe

5) If your service is apache:
# service httpd stop

6) Disable the volume group
# vgchange -a n <volume group name>

7) Physical Volume Resize
# pvresize /dev/sdb1

7.1) If you check your physical volume now you should see the free extents:
# pvdisplay

8) Re-enable the volume group
# vgchange -a y <vg name>

9) Re-mount the device
# mount /var/www (for example) or mount -a

10) Restart your service
# service httpd start

11) Now note that we've only expanded the Volume Group and neither has the Logical Volume or the File System been extended, but we can do these on the fly so it's o.k. if they are mounted.
# lvextend -l +<num of free extents> /dev/<vg name>/<lv name>

13) Resize the filesystem
# resize2fs /dev/<vg name>/<lv name>

In our case we find that it's helpful to test these procedures on clones and ensuring we have the most appropriate technique for the situation.

Extending root partition on the fly - linux on vmware

You've extended your VM's only disk by a bunch of Gigabytes.  You have Apache / MySQL running on it and you can't afford any downtime.  You now need the Operating System to recognize all that new space.  What can you do?  Expanding a root partition at runtime with a guest linux OS, requires a bit of planning but is still fairly straightforward.

The following was performed on a CentOS 5.5 Guest VM running on VMWare.

Let's see how much space we have right now:

[root@... ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                       18G   11G  6.5G  61% /
/dev/sda1              99M   13M   82M  14% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm

First, make sure the OS can recognize that the hardware actually changed.  Rescan your SCSI device:

# echo "1" > /sys/class/scsi_device/<device number>/device/rescan

Next comes the fun part.  This is where planning for disaster comes in handy; so even though you don't want to take any downtime, plan for it:  Take a snapshot of your VM.

Format your device and add a new partition.  In my case I have a /boot partition and a / partition so my new partition will have number 3 or /dev/sda3.

# fdisk /dev/sda

-- if we now try to create a new physical volume, it should fail until we run the partprobe command.

# partprobe

UPDATE: Since RedHat 6 (CentOS 6), you can use the partx command to force the changes to take effect on the partition table.  Note that partx does not do the same validation as partprobe, so if you've made mistakes with your partition layout, data can be erased.  If you are certain that your layout is correct, then proceed using:

# partx -l /dev/sda


And to force changes to take effect:

# partx -v -a /dev/sda

( See RedHat's recommendation at: https://access.redhat.com/site/solutions/57542 )

-- Create a physical volume from the new partition now that the kernel knows about it.

# pvcreate /dev/sda3

-- Extend the volume group to use up all space on the new physical volume.

# vgextend VolGroup00 /dev/sda3

-- Extend the logical volume by the number of free physical extents available in the group (use +)

# lvextend -l +3200 /dev/VolGroup00/LogVol00

-- Finally run an online resize of the mounted partition without affecting anything.

# resize2fs /dev/VolGroup00/LogVol00

That's it.  Now run df -h:

[root@... ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      115G   11G   99G  10% /
/dev/sda1              99M   13M   82M  14% /boot
tmpfs                 2.0G     0  2.0G   0% /dev/shm


----------------- EXTENDING A SWAP PARTITION -----------------

If you are doing this on a SWAP partition, then make sure you follow these instructions:

After extending the VolumeGroup, disable your swap:

[root@... ~]# swapoff -a

Extend your swap logical partition ( by 320 Physical Extents in my case ):

[root@... ~]# lvextend -l +320 /dev/VolGroup00/LogVol01

Check your logical volume size:

[root@... ~]# lvdisplay /dev/VolGroup00/LogVol01
  --- Logical volume ---
  LV Name                /dev/VolGroup00/LogVol01
  VG Name                VolGroup00
  LV UUID                --- ---- ---- --- ----
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                11.97 GB
  Current LE             383
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1

Use mkswap to recreate a new swap partition.  There is no need to worry about the data because when swap is disabled, it should not contain any data.

[root@... ~]# mkswap /dev/VolGroup00/LogVol01
Setting up swapspace version 1, size = 12851343 kB

Now restart your swap and check your memory:

[root@... ~]# swapon -a

[root@... ~]# free -m
             total       used       free     shared    buffers     cached
Mem:         24106       2917      21188          0        371        484
-/+ buffers/cache:       2061      22045
Swap:        12255          0      12255

Activate memory in Linux at run time using bash - vmware

In following with my previous post about "Adding scsi device at runtime on linux guest VM," I am adding some information here on how to use a bash "for-loop" to activate memory; it was added at runtime on a VMWare guest.

I've tested this on a CentOS 5.5 system.

First, add the new memory using VMWare VSphere.

Second, find the new memory that is currently listed as "offline".

[root@... ~]# grep offline /sys/devices/system/memory/*/state
/sys/devices/system/memory/memory40/state:offline
/sys/devices/system/memory/memory41/state:offline
/sys/devices/system/memory/memory42/state:offline
/sys/devices/system/memory/memory43/state:offline
/sys/devices/system/memory/memory44/state:offline
/sys/devices/system/memory/memory45/state:offline
/sys/devices/system/memory/memory46/state:offline
/sys/devices/system/memory/memory47/state:offline
/sys/devices/system/memory/memory48/state:offline
/sys/devices/system/memory/memory49/state:offline
/sys/devices/system/memory/memory50/state:offline
/sys/devices/system/memory/memory51/state:offline
/sys/devices/system/memory/memory52/state:offline
/sys/devices/system/memory/memory53/state:offline
/sys/devices/system/memory/memory54/state:offline
/sys/devices/system/memory/memory55/state:offline
/sys/devices/system/memory/memory56/state:offline
/sys/devices/system/memory/memory57/state:offline
/sys/devices/system/memory/memory58/state:offline
/sys/devices/system/memory/memory59/state:offline
/sys/devices/system/memory/memory60/state:offline
/sys/devices/system/memory/memory61/state:offline
/sys/devices/system/memory/memory62/state:offline
/sys/devices/system/memory/memory63/state:offline
/sys/devices/system/memory/memory64/state:offline
/sys/devices/system/memory/memory65/state:offline
/sys/devices/system/memory/memory66/state:offline
/sys/devices/system/memory/memory67/state:offline
/sys/devices/system/memory/memory68/state:offline
/sys/devices/system/memory/memory69/state:offline
/sys/devices/system/memory/memory70/state:offline
/sys/devices/system/memory/memory71/state:offline


Then, use a for loop to activate that memory:

[root@... ~]# for memcount in {40..71}; do echo online > /sys/devices/system/memory/memory$memcount/state; done


Check the new memory is active:

[root@... ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          8045        854       7190          0          8         87

Pre-allocating RAM on a Virtualbox guest

One of the problems with guest VMs in Virtualbox is that RAM is dynamically allocated by the host as the guest uses an increasing quantity of memory.  This is fine if you run many VMs which do not always need all the memory allocated to them at once; but you will find it inconvenient if you really need to allocate specific (read: large) amounts of memory to a VM.  This is especially true when running a guest on a host like windows 7, where superfetch has already allocated chunks of memory to different applications.  When the guest requests more memory, the OS does not give it, because it is only available to other programs which may not necessarily need it.

-- The solution then...

Forcing VirtualBox to "grab" all of the guest's memory at startup is possible.  This will attempt to allocate the entire guest memory from the host.  If that memory isn't really free, then the guest will not start at all.

There is a boolean flag which can be set as follows:

VBoxManage setextradata <VM NAME> VBoxInternal/RamPreAlloc 1

That's all.

Documentation: Unfortunately there is very poor documentation on the "VBoxInternal" keyset; probably because it is mainly used for development purposes and not necessarily "real" day-to-day use.  Consider this then, a hack.

The possible variables that can be set using VBoxInternal seem to be defined in the following C++ header file:

http://www.virtualbox.org/svn/vbox/trunk/src/VBox/VMM/include/PGMInternal.h

Here is another interesting file worth reading:

http://www.virtualbox.org/svn/vbox/trunk/include/VBox/err.h

I would be very careful with attempting to set any of these without a good understanding of the VirtualBox codebase.

Adding or resizing scsi device at runtime on linux guest VM

It's always a tricky thing to add more disk space to a VM when you don't want to take down it's services to reboot the box.  Linux doesn't need to be rebooted just to know that a new device has been attached, but how do you get it to recognize it?

As per a great blog post by Vivek Gite from NixCraft on: http://www.cyberciti.biz/tips/vmware-add-a-new-hard-disk-without-rebooting-guest.html

The basic command to re-scan scsi devices is:

echo "- - -" > /sys/class/scsi_host/<host#>/scan

fdisk -l

tail -f /var/log/message

If you do not have a new disk, but instead have increased the size of an existing disk, then you must rescan the device.  Note that this may not be appropriate if the device is used for the /boot partition.

# echo "1" > /sys/class/scsi_device/<device>/device/rescan

Parse Apache Logs by Date Range

Parsing apache logs by date and by date ranges can be fairly simple with a bit of awk scripting.

We use AWK to compare date fields in order to retrieve specific rows.

The date fields between access logs and error logs can vary, so some adjustments are needed:

Note that the date field is contained within a single column in the access_log file, therefore we can do a comparison against a single column.  Typically column #4.

AWK Date Range for access logs:

$ awk '$4>"[09/Aug/2012:15:00:" && $4<"[09/Aug/2012:15:59:"' ./access_log | less

The date field in the error log is in separate columns.  Example: [Thu Aug 09 15:30:...  That in itself is four columns.  They must be combined in order to be compared effectively.  To do this, we assign a combination of those four columns to two variables: $from and $two.  We then use these two variables for the comparison.  See below:

AWK Date Range for error logs:

$ awk '$from>"[Thu Aug 09 15:30:00" && $to<"[Thu Aug 09 15:59:00"' from='$1 " " $2 " " $3 " " $4' to='$1 " " $2 " " $3 " " $4' ./error_log | less

yum - Error: database disk image is malformed

If you've ever gotten this cryptic error using yum, you'll find that it's very difficult to pinpoint the cause. The message itself, "database disk image is malformed," refers to a corrupted sqlite file. However, the RPM and YUM systems use a variety of different such files; therefore finding the right one can be difficult.

The best thing to do, is to start by attempting to fix this using the available command line tool:

# yum clean all

This should solve the problem in most cases.  If the problem continues, perhaps the RPM database files are corrupted. One of my previous articles talks about rebuilding these, but I will go over it again here:

The database files are located in "/var/lib/rpm" and are named __db.001 __db.002 etc... etc...

Delete those files:

# rm -f /var/lib/rpm/__db*

Rebuild the database:

# rpm --rebuilddb

Then try to clean the yum cache as per the above command and try your yum command again.  If this continues to fail, try deleting your yum cache manually:

# rm -Rf /var/cache/yum

Now try the command again.  This should have gotten rid of the last sqlite files yum could possibly use.  The command should be able to rebuild all the databases correctly at this point.