20 Linux System Monitoring Tools Every SysAdmin Should Know

Need to monitor Linux server performance?

Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring.

These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem.

The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:

1. Finding out bottlenecks.
2. Disk (storage) bottlenecks.
3. CPU and memory bottlenecks.
4. Network bottlenecks.

#1: top - Process Activity Command

The top program provides a dynamic real-time view of a running system i.e. actual process activity. By default, it displays the most CPU-intensive tasks running on the server and updates the list every five seconds.

Fig.01: Linux top command

Commonly Used Hot Keys

The top command provides several useful hot keys:

Hot Key	Usage
t	Displays summary information off and on.
m	Displays memory information off and on.
A	Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system.
f	Enters an interactive configuration screen for top. Helpful for setting up top for a specific task.
o	Enables you to interactively select the ordering within top.
r	Issues renice command.
k	Issues kill command.
z	Turn on or off color/mono

=> Related: How do I Find Out Linux CPU Utilization?

#2: vmstat - System Activity, Hardware and System Information
The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.


# vmstat 3


Sample Outputs:

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 2540988 522188 5130400    0    0     2    32    4    2  4  1 96  0  0
 1  0      0 2540988 522188 5130400    0    0     0   720 1199  665  1  0 99  0  0
 0  0      0 2540956 522188 5130400    0    0     0     0 1151 1569  4  1 95  0  0
 0  0      0 2540956 522188 5130500    0    0     0     6 1117  439  1  0 99  0  0
 0  0      0 2540940 522188 5130512    0    0     0   536 1189  932  1  0 98  0  0
 0  0      0 2538444 522188 5130588    0    0     0     0 1187 1417  4  1 96  0  0
 0  0      0 2490060 522188 5130640    0    0     0    18 1253 1123  5  1 94  0  0

Display Memory Utilization Slabinfo

# vmstat -m


Get Information About Active / Inactive Memory Pages


# vmstat -a


=> Related: How do I find out Linux Resource utilization to detect system bottlenecks?

#3: w - Find Out Who Is Logged on And What They Are Doing
w command displays information about the users currently on the machine, and their processes.


# w username
# w vivek


Sample Outputs:

17:58:47 up 5 days, 20:28,  2 users,  load average: 0.36, 0.26, 0.24
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0    10.1.3.145       14:55    5.00s  0.04s  0.02s vim /etc/resolv.conf
root     pts/1    10.1.3.145       17:43    0.00s  0.03s  0.00s w

#4: uptime - Tell How Long The System Has Been Running

The uptime command can be used to see how long the server has been running. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.


# uptime


Output:

18:02:41 up 41 days, 23:42,  1 user,  load average: 0.00, 0.00, 0.00

1 can be considered as optimal load value. The load can change from system to system. For a single CPU system 1 - 3 and SMP systems 6-10 load value might be acceptable.

#5: ps - Displays The Processes

ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:


# ps -A


Sample Outputs:

PID TTY          TIME CMD
    1 ?        00:00:02 init
    2 ?        00:00:02 migration/0
    3 ?        00:00:01 ksoftirqd/0
    4 ?        00:00:00 watchdog/0
    5 ?        00:00:00 migration/1
    6 ?        00:00:15 ksoftirqd/1
....
.....
 4881 ?        00:53:28 java
 4885 tty1     00:00:00 mingetty
 4886 tty2     00:00:00 mingetty
 4887 tty3     00:00:00 mingetty
 4888 tty4     00:00:00 mingetty
 4891 tty5     00:00:00 mingetty
 4892 tty6     00:00:00 mingetty
 4893 ttyS1    00:00:00 agetty
12853 ?        00:00:00 cifsoplockd
12854 ?        00:00:00 cifsdnotifyd
14231 ?        00:10:34 lighttpd
14232 ?        00:00:00 php-cgi
54981 pts/0    00:00:00 vim
55465 ?        00:00:00 php-cgi
55546 ?        00:00:00 bind9-snmp-stat
55704 pts/1    00:00:00 ps

ps is just like top but provides more information.

Show Long Format Output


# ps -Al


To turn on extra full mode (it will show command line arguments passed to process):


# ps -AlF


To See Threads ( LWP and NLWP)


# ps -AlFH


To See Threads After Processes


# ps -AlLm


Print All Process On The Server


# ps ax
# ps axu


Print A Process Tree


# ps -ejH
# ps axjf
# pstree


Print Security Information


# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eM


See Every Process Running As User Vivek


# ps -U vivek -u vivek u


Set Output In a User-Defined Format


# ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
# ps axo stat,euid,ruid,tty,tpgid,sess,pgrp,ppid,pid,pcpu,comm
# ps -eopid,tt,user,fname,tmout,f,wchan


Display Only The Process IDs of Lighttpd


# ps -C lighttpd -o pid=


OR


# pgrep lighttpd


OR


# pgrep -u vivek php-cgi


Display The Name of PID 55977


# ps -p 55977 -o comm=


Find Out The Top 10 Memory Consuming Process


# ps -auxf | sort -nr -k 4 | head -10


Find Out top 10 CPU Consuming Process


# ps -auxf | sort -nr -k 3 | head -10


#6: free - Memory Usage
The command free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.


# free


Sample Output:

total       used       free     shared    buffers     cached
Mem:      12302896    9739664    2563232          0     523124    5154740
-/+ buffers/cache:    4061800    8241096
Swap:      1052248          0    1052248

=> Related: :

1. Linux Find Out Virtual Memory PAGESIZE
2. Linux Limit CPU Usage Per Process
3. How much RAM does my Ubuntu / Fedora Linux desktop PC have?

#7: iostat - Average CPU Load, Disk Activity

The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).

# iostat


Sample Outputs:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)  06/26/2009

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.50    0.09    0.51    0.03    0.00   95.86

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              22.04        31.88       512.03   16193351  260102868
sda1              0.00         0.00         0.00       2166        180
sda2             22.04        31.87       512.03   16189010  260102688
sda3              0.00         0.00         0.00       1615          0

=> Related: : Linux Track NFS Directory / Disk I/O Stats

#8: sar - Collect and Report System Activity
The sar command is used to collect, report, and save system activity information. To see network counter, enter:


# sar -n DEV | more


To display the network counters from the 24th:


# sar -n DEV -f /var/log/sa/sa24 | more


You can also display real time usage using sar:


# sar 4 5


Sample Outputs:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)   06/26/2009

06:45:12 PM       CPU     %user     %nice   %system   %iowait    %steal     %idle
06:45:16 PM       all      2.00      0.00      0.22      0.00      0.00     97.78
06:45:20 PM       all      2.07      0.00      0.38      0.03      0.00     97.52
06:45:24 PM       all      0.94      0.00      0.28      0.00      0.00     98.78
06:45:28 PM       all      1.56      0.00      0.22      0.00      0.00     98.22
06:45:32 PM       all      3.53      0.00      0.25      0.03      0.00     96.19
Average:          all      2.02      0.00      0.27      0.01      0.00     97.70

=> Related: : How to collect Linux system utilization data into a file

#9: mpstat - Multiprocessor Usage
The mpstat command displays activities for each available processor, processor 0 being the first one. mpstat -P ALL to display average CPU utilization per processor:


# mpstat -P ALL


Sample Output:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)   06/26/2009

06:48:11 PM  CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal   %idle    intr/s
06:48:11 PM  all    3.50    0.09    0.34    0.03    0.01    0.17    0.00   95.86   1218.04
06:48:11 PM    0    3.44    0.08    0.31    0.02    0.00    0.12    0.00   96.04   1000.31
06:48:11 PM    1    3.10    0.08    0.32    0.09    0.02    0.11    0.00   96.28     34.93
06:48:11 PM    2    4.16    0.11    0.36    0.02    0.00    0.11    0.00   95.25      0.00
06:48:11 PM    3    3.77    0.11    0.38    0.03    0.01    0.24    0.00   95.46     44.80
06:48:11 PM    4    2.96    0.07    0.29    0.04    0.02    0.10    0.00   96.52     25.91
06:48:11 PM    5    3.26    0.08    0.28    0.03    0.01    0.10    0.00   96.23     14.98
06:48:11 PM    6    4.00    0.10    0.34    0.01    0.00    0.13    0.00   95.42      3.75
06:48:11 PM    7    3.30    0.11    0.39    0.03    0.01    0.46    0.00   95.69     76.89

=> Related: : Linux display each multiple SMP CPU processors utilization individually.

#10: pmap - Process Memory Usage
The command pmap report memory map of a process. Use this command to find out causes of memory bottlenecks.


# pmap -d PID


To display process memory information for pid # 47394, enter:


# pmap -d 47394


Sample Outputs:

47394:   /usr/bin/php-cgi
Address           Kbytes Mode  Offset           Device    Mapping
0000000000400000    2584 r-x-- 0000000000000000 008:00002 php-cgi
0000000000886000     140 rw--- 0000000000286000 008:00002 php-cgi
00000000008a9000      52 rw--- 00000000008a9000 000:00000   [ anon ]
0000000000aa8000      76 rw--- 00000000002a8000 008:00002 php-cgi
000000000f678000    1980 rw--- 000000000f678000 000:00000   [ anon ]
000000314a600000     112 r-x-- 0000000000000000 008:00002 ld-2.5.so
000000314a81b000       4 r---- 000000000001b000 008:00002 ld-2.5.so
000000314a81c000       4 rw--- 000000000001c000 008:00002 ld-2.5.so
000000314aa00000    1328 r-x-- 0000000000000000 008:00002 libc-2.5.so
000000314ab4c000    2048 ----- 000000000014c000 008:00002 libc-2.5.so
.....
......
..
00002af8d48fd000       4 rw--- 0000000000006000 008:00002 xsl.so
00002af8d490c000      40 r-x-- 0000000000000000 008:00002 libnss_files-2.5.so
00002af8d4916000    2044 ----- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b15000       4 r---- 0000000000009000 008:00002 libnss_files-2.5.so
00002af8d4b16000       4 rw--- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b17000  768000 rw-s- 0000000000000000 000:00009 zero (deleted)
00007fffc95fe000      84 rw--- 00007ffffffea000 000:00000   [ stack ]
ffffffffff600000    8192 ----- 0000000000000000 000:00000   [ anon ]
mapped: 933712K    writeable/private: 4304K    shared: 768000K

The last line is very important:

• mapped: 933712K total amount of memory mapped to files
• writeable/private: 4304K the amount of private address space
• shared: 768000K the amount of address space this process is sharing with others

=> Related: : Linux find the memory used by a program / process using pmap command

#11 and #12: netstat and ss - Network Statistics
The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. ss command is used to dump socket statistics.

It allows showing information similar to netstat. See the following resources about ss and netstat commands:

• ss: Display Linux TCP / UDP Network and Socket Information
• Get Detailed Information About Particular IP address Connections Using netstat Command

#13: iptraf - Real-time Network Statistics

The iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others.

It can provide the following info in easy to read format:

• Network traffic statistics by TCP connection
• IP traffic statistics by network interface
• Network traffic statistics by protocol
• Network traffic statistics by TCP/UDP port and by packet size
• Network traffic statistics by Layer2 address

Fig.02: General interface statistics: IP traffic statistics by network interface

Fig.03 Network traffic statistics by TCP connection

#14: tcpdump - Detailed Network Traffic Analysis

The tcpdump is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool.

For.e.g to display traffic info about DNS, enter:


# tcpdump -i eth1 'udp port 53'


To display all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets, enter:


# tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'


To display all FTP session to 202.54.1.5, enter:


# tcpdump -i eth1 'dst 202.54.1.5 and (port 21 or 20'


To display all HTTP session to 192.168.1.5:


# tcpdump -ni eth0 'dst 192.168.1.5 and tcp and port http'


Use wireshark to view detailed information about files, enter:


# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80


#15: strace - System Calls
Trace system calls and signals. This is useful for debugging webserver and other server problems. See how to use to trace the process and see What it is doing.

#16: /Proc file system - Various Kernel Statistics
/proc file system provides detailed information about various hardware devices and other Linux kernel information.

See Linux kernel /proc documentations for further details. Common /proc examples:


# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts


17#: Nagios - Server And Network Monitoring
Nagios is a popular open source computer system and network monitoring application software. You can easily monitor all your hosts, network equipment and services.

It can send alert when things go wrong and again when they get better. FAN is "Fully Automated Nagios". FAN goals are to provide a Nagios installation including most tools provided by the Nagios Community.

FAN provides a CDRom image in the standard ISO format, making it easy to easilly install a Nagios server.

Added to this, a wide bunch of tools are including to the distribution, in order to improve the user experience around Nagios.

18#: Cacti - Web-based Monitoring Tool
Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality.

Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box.

All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices.

It can provide data about network, CPU, memory, logged in users, Apache, DNS servers and much more.

See how to install and configure Cacti network graphing tool under CentOS / RHEL.

#19: KDE System Guard - Real-time Systems Reporting and Graphing
KSysguard is a network enabled task and system monitor application for KDE desktop. This tool can be run over ssh session.

It provides lots of features such as a client/server architecture that enables monitoring of local and remote hosts.

The graphical front end uses so-called sensors to retrieve the information it displays. A sensor can return simple values or more complex information like tables.

For each type of information, one or more displays are provided. Displays are organized in worksheets that can be saved and loaded independently from each other. So, KSysguard is not only a simple task manager but also a very powerful tool to control large server farms.

Fig.05 KDE System Guard {Image credit: Wikipedia}

See the KSysguard handbook for detailed usage.

#20: Gnome System Monitor - Real-time Systems Reporting and Graphing
The System Monitor application enables you to display basic system information and monitor system processes, usage of system resources, and file systems.

You can also use System Monitor to modify the behavior of your system. Although not as powerful as the KDE System Guard, it provides the basic information which may be useful for new users:

• Displays various basic information about the computer's hardware and software.
• Linux Kernel version
• GNOME version
• Hardware
• Installed memory
• Processors and speeds
• System Status
• Currently available disk space
• Processes
• Memory and swap space
• Network usage
• File Systems
• Lists all mounted filesystems along with basic information about each.

Fig.06 The Gnome System Monitor application

Bounce: Additional Tools

A few more tools:

• nmap - scan your server for open ports.
• lsof - list open files, network connections and much more.
• ntop web based tool - ntop is the best tool to see network usage in a way similar to what top command does for processes i.e. it is network traffic monitoring software. You can see network status, protocol wise distribution of traffic for UDP, TCP, DNS, HTTP and other protocols.
• Conky - Another good monitoring tool for the X Window System. It is highly configurable and is able to monitor many system variables including the status of the CPU, memory, swap space, disk storage, temperatures, processes, network interfaces, battery power, system messages, e-mail inboxes etc.
• GKrellM - It can be used to monitor the status of CPUs, main memory, hard disks, network interfaces, local and remote mailboxes, and many other things.
• vnstat - vnStat is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s).
• htop - htop is an enhanced version of top, the interactive process viewer, which can display the list of processes in a tree form.
• mtr - mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

Did I miss something? Please add your favorite system motoring tool in the comments.

Top 5 Linux Video Editor Software

I'm looking for a free video editor similar to - Adobe Premiere Pro, Apple iMovie, Final Cut Pro or Microsoft Movie Maker under Linux Desktop operating system.

My tasks are pretty simple such as cutting, filtering, and encoding tasks etc. Can you provide me a list of FOSS software which can be used for video capture and video editing purposes under Fedora or Ubuntu Linux desktop systems?

A non-linear editing system (NLE) is a video editing (NLVE) or audio editing (NLAE) system which can provide editing method for video clips or frams.

You will be able to access any frame in a video clip. Non-linear editing is done for film and television post-production.

However, the cost of editing system gone down and non-linear editing tools (including software) are now within the reach of most home users.

MS-Windows PC included Windows Movie Maker and Apple computer comes with iMovie. Most Linux based editing software can now be downloaded free of charge from the Internet.

You also need a video capture card and a FireWire connection to capture digital video from a DV camera.

Avidemux
Avidemux is a free video editor designed for simple cutting, filtering and encoding tasks. It supports many file types, including AVI, DVD compatible MPEG files, MP4 and ASF, using a variety of codecs.

Tasks can be automated using projects, job queue and powerful scripting capabilities. Avidemux is available for Linux, BSD, Mac OS X and Microsoft Windows under the GNU GPL license.

Fig.01: Avidemux in Action under Ubuntu (image credit: Wikipedia)

How Do I Install Avidemux Under Debian / Ubuntu Linux Desktop?

Type the following command:


$ sudp apt-get install avidemux

Embedding The Subtitles to AVI By Using Avidemux

=> Download Avidemux

Cinelerra
Cinelerra is the most advanced non-linear video editor and compositor for Linux. Cinelerra also includes a video compositing engine, allowing the user to perform common compositing operations such as keying and mattes.

Cinelerra includes support for very high-fidelity audio and video: it processes audio using 64 bits of precision, and can work in both RGBA and YUVA color spaces, using floating-point and 16-bit integer representations, respectively.

It is resolution and frame rate-independent, meaning that it can support video of any speed and size.

Fig.02: Cinelerra Rendering in Action (credit Cinelerra project)

Video editing in Ubuntu Using Cinelerra Part 1

Cinelerra Tutorial Capturing Desktop Screens

=> Download Cinelerra

Kdenlive

Kdenlive is an intuitive and powerful multi-track video editor, including most recent video technologies. Kdenlive supports all of the formats supported by FFmpeg (such as QuickTime, AVI, WMV, MPEG, and Flash Video), and also supports 4:3 and 16:9 aspect ratios for both PAL, NTSC and various HD standards, including HDV.

Video can also be exported to DV devices, or written to a DVD with chapters and a simple menu. Kdenlive packages are freely available for GNU/Linux, FreeBSD and Mac OS X under the terms of GNU General Public License version 2 or any version later.

Fig.03: Kdenlive in Action (credit: Kdenlive project)

How Do I Install Kdenlive Under Debian / Ubuntu Linux Desktop?

Type the following command:

$ sudp apt-get install kdenlive


Video Effects & Stacking - Kdenlive 0.7 - Ubuntu 8.10

=> Download Kdenlive

Kino

Kino is a non-linear DV editor for GNU/Linux. It features excellent integration with IEEE-1394 for capture, VTR control, and recording back to the camera. It captures video to disk in Raw DV and AVI format, in both type-1 DV and type-2 DV (separate audio stream) encodings.

Fig.04: Kino Main Window (image credit - Kino porject)

How Do I Install Kino Under Debian / Ubuntu Linux Desktop?

Type the following command:


$ sudp apt-get install kino


LINUX video capture - KINO Tutorial

=> Download Kino

LiVES

LiVES (LiVES is a Video Editing System) is a free software video editing program and VJ tool. LiVES mixes realtime video performance and non-linear editing in one professional quality application.

It will let you start editing and making video right away, without having to worry about formats, frame sizes, or framerates.

It is a very flexible tool which is used by both professional VJ's and video editors - mix and switch clips from the keyboard, use dozens of realtime effects, trim and edit your clips in the clip editor, and bring them together using the multitrack timeline.

You can even record your performance in real time, and then edit it further or render it straight away.

For the more technically minded, the application is frame and sample accurate, and it can be controlled remotely or scripted for use as a video server. And it supports all of the latest free standards.

Fig.05: Lives: Linux Video Editing System (Image: Lives project)

Demo made using LiVES Software

=> Download LiVES

Comparison Of Video Editing Software

Feature	Avidemux	Cinelerra	Kdenlive	Kino	LiVES
License	GPL	GPL	GPLv2	GPL	GPLv3+
Cost	Free	Free	Free	Free	Free
Paid Support	N	Y	N	N	N
RAM (min)	?	256M	256M	?	128M
Hard Disk (min)	?	?	1G	?	10G
CPU	?	500Mhz	600Mhz	?	800Mhz
High Definition Video Editing	?	Y	Y	?	Y
Non-destructive Editing	?	Y	Y	Y	Y
Full-screen Playback	?	Y	Y	Y	Y
Storyboard Mode	?	N	Y	Y	N
Video Tracks	Y	Y	Y	?	Y
Audio Tracks	Y	Y	Y	?	Y
Linear Timecode Display	?	Y	Y	?	Y
DVD Output	?	Y	Y	N	Y
HD Output	?	Y	Y	N	Y
Smart Phone Output	?	Y	Y	N	Y
QuickTime Output	?	Y	Y	N	Y
Windows Media Output	?	Y	Y	N	Y
MPEG-4 Output	?	Y	Y	Y	Y
Web Output	?	Y	Y	N	N

Other Open Source Non-linear Video Editing Software For Linux Operating Systems

1. Blender - 3D animation suite (cross-platform) : Blender is a 3D graphics application. It can be used for modeling, UV unwrapping, texturing, rigging, water simulations, skinning, animating, rendering, particle and other simulations, non-linear editing, compositing, and creating interactive 3D applications, including games. Blender's features include advanced simulation tools such as rigid body, fluid, cloth and softbody dynamics, modifier based modeling tools, powerful character animation tools, a node based material and compositing system and Python for embedded scripting.
2. OpenShot Video Editor : OpenShot Video Editor is an open-source program that creates, modifies, and edits video files.
3. PiTiVi : PiTiVi is a program for video editing based on the GStreamer framework. It can - Capture and encode audio and video, with formats supported by GStreamer, split and trim video clips, split and trim audio, render projects in any format supported by the GStreamer framework etc.

Our Recommendation

• Use Cinelerra for professional work. It is very fast, and can handle a heavy load. You can also obtain paid support for this product.
• For video encoding and conversion purpose use Avidemux.

Who Uses...?

1. Cinelerra - Recommended for Animator, Artist/Illustrator/Designer, video editor.
2. Kino - Recommended of home user, video editor, and videographer.
3. Avidemux (Non-Linear Editor) - Recommended videographer
4. Kdenlive - Recommended for home user.
5. LiVES - Recommend for home user and VJ.

What Software do you use for Digital Video Editing?

Learn to use extended file attributes in Linux to boost security

ACLs and extended attributes for files are simple and easy to use in Linux, and can go a long way in securing files. Vincent Danen goes over some of the basic file protection enhancements provided by the Linux kernel.
—————————————————————————————

With all the talk of enhanced file system security and security frameworks, some of the basic file protection enhancements provided by the Linux kernel have been forgotten.

While there is certainly a distinct place for security applications like SELinux, GrSecurity and others, there are simple means for securing files as well. ACLs and extended attributes for files are simple and easy to use, and can go a long way in securing files.

The first tools to use with extended attributes is chattr, which changes file attributes for files, and lsattr which lists those attributes.

There are a number of extended attributes you can add or remove from files, including “a”, which makes a file append-only, and “i” which makes a file immutable (cannot be modified, deleted, or renamed, nor can any link be created to the file).

There are other attributes that deal with compression, undeletion, secure deletion, and journaling as well.

By default, only the root user can change these extended attributes. If you want to allow users to set and remove these extended attributes, you must mount the filesystem with the user_xattr mount option:

UUID=661ab9f1-c381-4962-bcfc-0b5e2aab1ce9 /home                   ext4    defaults,user_xattr,acl        1 2

The other tools that can set and list attributes are the setfattr and getfattr programs. These are useful with programs like Beagle that store certain metadata with files, but they can be useful outside of these applications as well.

These don’t have much to do with security, but they are useful nonetheless:

$ setfattr -n user.comment -v "this is a comment" testfile

$ getfattr testfile

# file: testfile

user.comment

$ getfattr -n user.comment testfile

# file: testfile

user.comment="this is a comment"

Finally, to set ACLs (Access Control Lists) on files, use the setfacl and getfacl tools. In order to use these commands, and ACLs in general, the filesystem must be mounted with the acl mount option.

Traditionally, files have three distinct access controls: read, write, and execute, and they are for three distinct groups: user, group, and other (or world).

If you wanted to have two or three people have write access to a file, you would have to create a group that all people were members of, give the file appropriate group ownership, and make it writable by the group.

With ACLs, you can bypass the need for creating groups in this fashion.

For instance, if you create a file that is owned joe:joe with 0644 permissions (read/write to joe, read-only to everyone else), only Joe can edit it.

If you want Angela to have access to write to this file, but no one else, ACLs can help:

$ setfacl -m u:angela:rw testfile

$ getfacl testfile

# file: testfile

# owner: joe

# group: joe

user::rw-

user:angela:rw-

group::r--

mask::rw-

other::r--

% ls -al testfile

-rw-rw-r--+ 1 joe    joe    6 2009-11-11 14:28 testfile

The above modifies the ACLs on the file testfile and adds an ACL for the user angela and gives her read/write (rw) permissions.

Using getfacl, it is obvious that angela has rw permissions, as does joe. When using ls, you can also see that the file has an ACL associated with it due to the + in the permissions and attributes string.

Now this file can be edited by joe and angela, and no one else, despite it being owned by the user and group joe.

This is, of course, a brief introduction to ACLs and extended attributes. The manpages for getfacl, setfacl, chattr, lsattr, getfattr, and setfattr all explain the various options, ACLs, and attributes.

All of these options should work on any filesystem in recent kernels, provided they are mounted with the appropriate acl and user_xattr options.