Linux Audit Files to See Who Made Changes to a File

Linux audit files to see who made changes to a file

http://www.cyberciti.biz/tips/linux-audit-files-to-see-who-made-changes-to-a-file.html[5/11/2013 1:58:18 ]

Linux audit files to see who made changes to a fileby NIXCRAFT on MARCH 19, 2007 48 COMMENTS LAST UPDATED SEPTEMBER 7, 2007

in FILE SYSTEM , GNU/OPEN SOURCE, HOWTO

This is one of the key questions many new sys admin ask:

How do I audit file events such as read / write etc? How can I use audit tosee who changed a file in Linux?

The answer is to use 2.6 kernels audit system. Modern Linux kernel(2.6.x) comes with auditd daemon. Its responsible for writing audit recordsto the disk. During startup, the rules in /etc/audit.rules are read by this daemon. You can open/etc/audit.rules file and make changes such as setup audit file log location and other option.The default file is good enough to get started with auditd.

In order to use audit facility you need to use following utilities=> auditctl - a command to assist controlling the kernels audit system. You can get status,and add or delete rules into kernel audit system. Setting a watch on a file is accomplishedusing this command:

=> ausearch - a command that can query the audit daemon logs based for events based ondifferent search criteria.

=> aureport - a tool that produces summary reports of the audit system logs.

Note that following all instructions are tested on CentOS 4.x and Fedora Core and RHEL 4/5Linux.

Task: install audit packageThe audit package contains the user space utilities for storing and searching the audit recordsgenerate by the audit subsystem in the Linux 2.6 kernel. CentOS/Red Hat and Fedora coreincludes audit rpm package. Use yum or up2date command to install package

or

Auto start auditd service on boot

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nixCraft: 40.146 .nixCraft: 40.146 .

nixCraft

! !

! ! .

# yum install audit

# up2date install audit

# ntsysv

A B O U T F O R U M H O W T O S & F A Q S L O W G R A P H I C S S H E L L S C R I P T S R S S / F E E D



OR

Now start service:

How do I set a watch on a file for auditing?Let us say you would like to audit a /etc/passwd file. You need to type command as follows:

Where,

-w /etc/passwd : Insert a watch for the file system object at given path i.e. watch filecalled /etc/passwd-p war : Set permissions filter for a file system watch. It can be r for read, w for write, x forexecute, a for append.-k password-file : Set a filter key on a /etc/passwd file (watch). The password-file is afilterkey (string of text that can be up to 31 bytes long). It can uniquely identify the auditrecords produced by the watch. You need to use password-file string or phrase whilesearching audit logs.

In short you are monitoring (read as watching) a /etc/passwd file for anyone (including syscall)that may perform a write, append or read operation on a file.

Wait for some time or as a normal user run command as follows:

Following are more examples:

File System audit rules

Add a watch on "/etc/shadow" with the arbitrary filterkey "shadow-file" that generates recordsfor "reads, writes, executes, and appends" on "shadow"

syscall audit ruleThe next rule suppresses auditing for mount syscall exits

File system audit ruleAdd a watch "tmp" with a NULL filterkey that generates records "executes" on "/tmp" (good fora webserver)

syscall audit rule using pidTo see all syscalls made by a program called sshd (pid - 1005):

R E L A T E D P O S T S

# chkconfig auditd on

# /etc/init.d/auditd start

# auditctl -w /etc/passwd -p war -k password-file

$ grep 'something' /etc/passwd$ vi /etc/passwd

# auditctl -w /etc/shadow -k shadow-file -p rwxa

# auditctl -a exit,never -S mount

# auditctl -w /tmp -p e -k webserver-watch-tmp

# auditctl -a entry,always -S all -F pid=1005

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How do I find out who changed or accessed a file/etc/passwd?Use ausearch command as follows:

OR

OR

Where,

-f /etc/passwd : Only search for this file-i : Interpret numeric entities into text. For example, uid is converted to account name.

Output:

Let us try to understand output

audit(03/16/2007 14:52:59.985:55) : Audit log timeuid=lighttpd gid=lighttpd : User ids in numerical format. By passing -i option tocommand you can convert most of numeric data to human readable format. In our exampleuser is lighttpd used grep command to open a fileexe="/bin/grep" : Command grep used to access /etc/passwd fileperm_mask=read : File was open for read operation

So from log files you can clearly see who read file using grep or made changes to a file usingvi/vim text editor. Log provides tons of other information. You need to read man pages anddocumentation to understand raw log format.

Other useful examples

Search for events with date and time stamps. if the date is omitted, today is assumed. If thetime is omitted, now is assumed. Use 24 hour clock time rather than AM or PM to specify time.An example date is 10/24/05. An example of time is 18:00:00.

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# ausearch -f /etc/passwd

# ausearch -f /etc/passwd | less

# ausearch -f /etc/passwd -i | less

----type=PATH msg=audit(03/16/2007 14:52:59.985:55) : name=/etc/passwd flags=follow,open inode=23087346 dev=08:02 mode=file,644 ouid=root ogid=root rdev=00:00type=CWD msg=audit(03/16/2007 14:52:59.985:55) : cwd=/webroot/home/lighttpdtype=FS_INODE msg=audit(03/16/2007 14:52:59.985:55) : inode=23087346 inode_uid=root inode_gid=root inode_dev=08:02 inode_rdev=00:00type=FS_WATCH msg=audit(03/16/2007 14:52:59.985:55) : watch_inode=23087346 watch=passwd filterkey=password-file perm=read,write,append perm_mask=readtype=SYSCALL msg=audit(03/16/2007 14:52:59.985:55) : arch=x86_64 syscall=open success=yes exit=3 a0=7fbffffcb4 a1=0 a2=2 a3=6171d0 items=1 pid=12551 auid=unknown(4294967295) uid=lighttpd gid=lighttpd euid=lighttpd suid=lighttpd fsuid=lighttpd egid=lighttpd sgid=lighttpd fsgid=lighttpd comm=grep exe=/bin/grep

# ausearch -ts today -k password-file



Tweet 44 11 !

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Search for an event matching the given executable name using -x option. For example find outwho has accessed /etc/passwd using rm command:

Search for an event with the given user name (UID). For example find out if user vivek (uid506) try to open /etc/passwd:

Other auditing related posts

How to keep a detailed audit trail of whats being done on your Linux systemsHow do I find out Linux CPU utilization?Linux Setting processor affinity for a certain task or process

Further readingsRead man pages - auditd, ausearch, auditctl

Updated for accuracy.

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# ausearch -ts 3/12/07 -k password-file

# ausearch -ts today -k password-file -x rm# ausearch -ts 3/12/07 -k password-file -x rm

# ausearch -ts today -k password-file -x rm -ui 506# ausearch -k password-file -ui 506

Cosmotewww.cosmote.gr

HTC online Cosmote!



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{ 48 comments read them below or add one }

James Musil March 21, 2007 at 3:42 pm

In the line auditctl -w /etc/passwd -k shadow-file -p rwxa you mean /etc/shadow not/etc/passwd.

REPLY

nixCraft March 21, 2007 at 4:41 pm

James,

Thanks for heads up, post has been updated.

REPLY

GH Snijders March 22, 2007 at 8:12 am

Very interesting article, thanks alot.

I did spot one small detail, though:

So from log files you can clearly see who made changes to a file using grep commands.

Grep is a tool to *read* files, not change them ;)

REPLY

nixCraft March 22, 2007 at 8:29 am

GH,

Heh I was suppose to use vim as an example but somehow I did pickup grep. Anyway posthas been updated

Appreciate your post.

REPLY

Rodrigo March 27, 2007 at 8:32 pm

Question, i need a file monitor to tell me which files are being used on a few folders, can iuse auditd? is it compatible with Redhat 7.3? is there a GUI to use with this?

If this is not what i need.. can you point me to what i need or something close?

REPLY

nixCraft March 28, 2007 at 5:54 am

Rodrigo,



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RH 7.3 does not support auditd; also a big security risk for such old disro.

Get Cent OS 4.x or FC 6/7

REPLY

Rodrigo March 28, 2007 at 11:29 am

Sadly the box running RH 7.3 is a live production box for a multinational company, I cant justget a new OS installed on that server, we will be at least another 6 months before migratingto a new system.

Do you perhaps have an idea of what tool I could use to monitor files in a folder that havebeen accessed during a period of time?

BTW great site.

REPLY

motumboe March 30, 2007 at 7:22 am

Found this article following this link: http://beranger.org/index.php?article=2722

Two great blogs, my comps:-)

REPLY

nixCraft March 30, 2007 at 5:26 pm

@motumboe, thanks for feedback :D

@Rodrigo you can write your own perl scripts

REPLY

Ken September 6, 2007 at 10:40 pm

When I try to set up a file watch, it fails. When I do an auditctl -l, i get this at the bottom:

File system watches not supported

Any ideas on whats wrong?

(btw, Im guessing that I can get around this by tracing syscalls based on the files inodenumbers, but thats messy, and hard to maintain)

REPLY

tiger74 January 25, 2008 at 2:23 am

@nixcraft,Thank you for such a great article.But, Im confused, it seems that there is no man page for the audit.rules?



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@rodrigo,You can use tripwire with similar function. It detects file changes.

REPLY

ike April 27, 2008 at 7:49 pm

:-) Wow. This is great article.

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Ken May 22, 2008 at 11:11 am

I got the same error:

File system watches not supported

Did you ever resolve this?

Thanks John

REPLY

Nguyen Dang December 14, 2008 at 12:50 am

Hi, thanks for the article.

How do I redirect auditd to not generate log message but call a user-defined program (for anselected event)? Is it possible?

Thank you very much.

REPLY

Relay February 11, 2009 at 7:03 pm

In the description for the -p option, a is for attribute, not append the man page has a fullexplaination.

-p war : Set permissions filter for a file system watch. It can be r for read, w for write, x forexecute, a for append.

REPLY

John Doe April 3, 2012 at 12:51 amNewer versions seem to use a for attribute changes, my manpage reads like this:

-p [r|w|x|a]Set permissions filter for a file system watch. r=read, w=write, x=execute, a=attributechange.

Nice article though, exactly what i needed. :)



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john May 9, 2009 at 12:09 pm

Great article. Ive checked the man pages and am still left with two questions:

1. It doesnt appear that the options to the p switch allow for logging file deletions? How dowe log when a file is deleted?

2. The kernel does not allow us set a watch on the / directory. If I wanted to log all filedeletions, would I be best served by setting watches on all my top level directories(bin,boot,dev,etc)?

Thanks again for the great resource!- John

REPLY

J.C. Denton July 3, 2009 at 3:44 pm

After a system restart or a manual one (sudo /etc/init.d/auditd restart) all my file monitoring isgone. sudo auditctl -l says no rules then. do I have to save the rules to a textfile orsomething? Please help (using (X)ubuntu 8.04 LTS)! ;-)

REPLY

Frans July 20, 2009 at 6:40 am

Is this also working on Vmware ESX server 3.5? Because this is a modified RedHatdistrobution.

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Stef November 12, 2009 at 9:28 am

Hi,

thanks for this article. Helps me a lot!

regards

REPLY

sushil December 18, 2009 at 5:15 pm

hello,good article..

REPLY

asdasdsd December 22, 2009 at 1:23 pm

# /etc/init.d/audit start



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# auditctl -w /etc/passwd -p war -k _etc_passwd# auditctl -w /etc/shadow -k etc_shadow -p rwxa# vipw (make a change)# ausearch -f etc_passwd

Not a lot of use this idea :(

REPLY

asdasdsd December 22, 2009 at 1:25 pm

/edit:# ausearch -f etc_passwd\

Had to escape the greater and less than sign because this comments section thought that itwas some HTML!

REPLY

Anonymous July 5, 2010 at 9:04 pm

is it possible to use it from NIS.. we use ypcat

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Jagadeesh July 9, 2010 at 5:07 am

Hi,

This is very nice article. In my company we have NFS mounted home directories. Anyonecan access files from anybodys home. This will help me monitoring who comes to my home:-)

Thanks for this article

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Hello1971 July 14, 2010 at 2:03 am

Hi, Did this work on exported directory. I mean, if any one read/write a file through NFS, Theaudit system will log them??

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nima0102 September 21, 2010 at 1:51 pm

Good Article :):)

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Dave Marcus October 7, 2010 at 9:07 pm

Is there anyway to place an audit on a directory? And yes its a very good article, I have it



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bookmarked.

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Yzhar November 11, 2010 at 10:27 amIm a Varins inc eng that had research this stuff for a while.

Unix (any), lacks such abilities and the best it can do is audit pre define objects.scale is poor and some file operations are missing.

We have successfully build such framework (for about any unix platforms).it is running on hundreds production sites for 3 years now. and I can tell you it wasnteasy.

I dont want to sound like a sales man (Im not), but hope I can save you some time ifyou are looking for such solution.

btw,very nice article.

REPLY

Aldian November 22, 2010 at 10:34 am

You forgot to explain how to stop monitoring once not needed anymore

REPLY

Sandy December 12, 2010 at 7:42 pm

Does auditd work over NFS ? . I mean, if any one read/write a file through NFS, The auditsystem will log them?? I have not been able to configure this. auditd captures read/writeaccess from FTP and even CIFS but not from NFS ? Anyone has any Clue ?

REPLY

Prashant October 17, 2011 at 5:48 amHi Sandy,

Were you about to get the answer for your query..As even I want to get statistics on NFS / CIFS / FTP etc..please let me know if you got any tips !

thnxPrashant

REPLY

Roumen Semov December 16, 2010 at 12:39 am

Hmmm, appending text to a watched file does not show up in the audit logs:echo hello world >> /etc/passwdAny idea why?



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RG May 27, 2011 at 5:00 amYou might need to turn auditing on by changing the default yes to noat the bottom of the file /etc/sysconfig/auditd:# This option disables syscall auditing by default. This can also be# accomplished by auditctl -e.AUDITD_DISABLE_CONTEXTS=noSet to no for full audit functionality including file and directory watches and system callauditing.

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DarenTay February 25, 2011 at 8:04 am

If a user su to root, how do we manage that? Can we identify whos the original user?

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joe March 21, 2011 at 5:43 pm

Daren TayFor SU install sudo and which uses su log.

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Cristian Rusu April 27, 2011 at 7:52 am

Hello

Is there any way to figure out what php script modified a file on the system?I got a bug where all the images in some folders are converted to an black empty png and Icant figure out what does this for months.

Thank you for any hint

Cris

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David May 23, 2011 at 9:35 pmId change the permissions on the PNG files to read-only possibly by changing theextended attributes if necessary and see what breaks. Might have to change thedirectory permissions if the mysterious program is actually creating a new file and movingdeleting the old one as these steps dont require file permissions, just directorypermissions.

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Tha_Duck May 26, 2011 at 11:38 am

# auditctl -w /tmp -p e -k webserver-watch-tmp



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Shouldnt that be:# auditctl -w /tmp -p x -k webserver-watch-tmp

?

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dreamingkat July 9, 2011 at 8:10 am

according to the man page, a isnt for append, its for attribute changes.

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Funutation October 13, 2011 at 5:45 pm

anyone know whether SELinux includes these features? I assume that it does, and doeseven more but I cannot find details (easily :-)

thanx

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ceooph November 21, 2011 at 9:15 am

Hi,Thanks for this article and your whole site. I have a problem with auditd.Can you audit a directory (yes) and all subdirectory ??I want to audit a complete map point with folder, sub-folder, sub-sub-folder,

Thanks a lot for your help

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John Gonzalez November 29, 2011 at 11:55 pm

Thank You!!!

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ritesh June 4, 2012 at 11:46 am

HI,I configured samba as a file server. Server is running successfully. I wanted to see logswhich user currently accessing a file and which file got deleted from user.Is this possible in samba ?Thanks in advacne.Ritesh

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thomas October 19, 2012 at 3:26 am

i have set up my audit.rules file.



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when i start auditd, i get an output stating:

the audit system is in immutable mode. no audit rules loaded.

when i type auditctl -l it says no rules loaded.

i thought when i set up my audit.rules file and started auditd, thats all i had to do. afterreading this article, i believe there is more i need to do.

can someone elaborate on how the audit.rules file comes into play?

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ibeam7 November 28, 2012 at 11:20 pmthomasCheck to see if you have-e 2at the end of your audit.rules file. If so, once you reload or restart your auditd service youwill not be able to modify your rules file without bouncing the server. If doing testing, itsbest to use-e 1which just enables the rules but doesnt lock them.

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Kirk March 26, 2013 at 11:14 pm

Is it possible to write rules to detect modifications to any file in /var/www with the namesettings.php? This doesnt work, but it captures what Id like to be able to do:

auditctl -w /var/www/vhosts/*/settings.php -k config-watch -prwa

Thanks.

REPLY

Sarfraz September 2, 2013 at 12:27 pm

Do we enable file auditing for files accessed from SFTP like winscp tool?

REPLY

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