/proc file system

One of the primary function of porc filesystem to control the access to physical devices on the

server and schedule when and how processes interact with these devices.

Under Linux, all data are stored as files. The /proc/ directory contains another type of file

called a virtual file. Hence, proc is known as virtual filesystem.

I have described some important proc files and directories here for system administration usage:

Some of the directories from /proc

Quote

asound
bus
driver
fs
ide
irq
net
sys
sysvipc
tty


Each time a new process is created, an entry in /proc is created.The name of the directory entry

corresponds to the process identification number (PID) of the created process, so, for example,

a process with a PID of 5985 will have a corresponding directory entry of /proc/5985/.

Note: /usr/bin/procinfo - Shows system status gathered from /proc

These directories are called process directories, as they refer to a process's ID and contain

information specific to that process

* cmdline — Contains the command line arguments that started the process.
* cpu — Provides specific information about the utilization of each of the system's CPUs
* cwd — A link to the current working directory for the process
* environ — Gives a list of the environment variables for the proces
* exe — A link to the executable of this process
* fd — A directory containing all of the file descriptors for a particular process
* maps — Contains memory maps to the various executables and library files associated

with this process.
* mem — The memory held by the process.
* root — A link to the root directory of the process
* stat — A status of the process
* statm — A status of the memory in use by the process
* status - Same as stat and statm but in formated way.

/proc/cmdline
The content of /proc/cmdline is the kernel parameters you pass during boot.
The easiest way to check which boot parameters are passed to the kernel is to execute cat

/proc/cpuinfo
Information about the processor, such as its type, make, model, and
performance.

/proc/devices
List of device drivers configured into the currently running kernel.

/proc/dma
Shows which DMA channels are being used at the moment.

/proc/filesystems
Filesystems configured into the kernel

/proc/interrupts
Shows which interrupts are in use, and how many of each there have been

/proc/ioports
Which I/O ports are in use at the moment.

/proc/loadavg
The /proc/loadavg file contains information about the system load. The first three numbers

represent the number of active tasks on the system—processes that are actually running

/proc/uptime
The /proc/uptime file contains the length of time since the system was booted, as well as the

amount of time since then that the system has been idle. Both are given as floating-point

values, in seconds.

/proc/ mdstat
The /proc/ mdstat file shows no active RAID devices:

/proc/meminfo
cat /proc/meminfo | grep MemTotal
This /proc/meminfo shows the memory status in the form of both high-level and low-level

statistics.

/proc/misc
Miscellaneous pieces of information. This is for information that has no real place within the

rest of the proc filesystem

/proc/modules
Kernel modules currently loaded. Same as 'lsmod' command

/proc/mounts
Shows the list of mounted filesystems

/proc/partitions
Shows all partitions in the disk.

/proc/pci
Information about pci bus

/proc/swaps
Display swap information.

/proc/version
The kernel version.

Netwok Parameter in /proc/net

/proc/net/arp - Display arp table. Similar to arp command.
/proc/net/dev - Shows network devices with statastics.
/proc/net/if_inet6 - List of IPv6 interface addresses
/proc/ip_tables_targets - Parameter shows related to Iptables
/proc/ip_tables_names - Parameter shows related to Iptables
/proc/netstat - network statatics configured at kernel level.
/proc/route - network route, use route command -n option.

/proc/sys/fs/file-max
Max file files Limit

# cat /proc/sys/fs/file-max
52224

/proc/sys/kernel/sysrq
System Request Key on a running kernel.

/proc/sys/kernel/acct
This file contains three numbers: highwater, lowwater and frequency. If BSD-style process

accounting is enabled these values control its behaviour. If free space on filesystem where the

log lives goes below lowwater percent accounting suspends. If free space gets above highwater

percent accounting resumes. Frequency determines how often the kernel checks the amount of free

space (value is in seconds). Default values are 4, 2 and 30. That is, suspend accounting if <=

2% of space is free; resume it if >= 4% of space is free; consider information about amount of

free space valid for 30 seconds.

/proc/sys/kernel/hostname
This file can be used to set the NIS/YP hostname in exactly the same way as the command

hostname.

/proc/sys/kernel/domainname
This file can be used to set the NIS/YP domainname in exactly the same way as the command

domainname

/proc/sys/kernel/osrelease
The running kernel version.

/proc/sys/kernel/ostype
Guess!!! what its Linux only

/proc/sys/kernel/version
Example: #2 SMP PREEMPT Sun May 21 10:47:59 CEST 2006
#2 means that this is the 2nd kernel built from this source base and the date after it indicates

the time the kernel was built. The only way to tune this info is to rebuild the kernel.


/proc/sys/net - All TCP and network configuration parameter for kernel.

Excluding specific file types using GNU tar

Excluding specific file types using GNU tar

You can specifically stop tar from archiving certain file types based on patterns (shell wildcards). For example, to archive everything in a directory excluding PDF and DOC files:

tar czvf archive.tgz --exclude=*.doc --exclude=*.pdf *

That creates a gzipped tarball with everything in the current directory and do not include PDF and DOC files. You can specify multiple --exclude parameters.

Common Linux Shell Commands

Common Linux Shell Commands:

ls : list files/directories in a directory, comparable to dir in windows/dos.
ls -al :[/b] shows all files (including ones that start with a period), directories, and details attributes for each file.

cd : change directory · · cd /usr/local/apache : go to /usr/local/apache/ directory
cd ~ : go to your home directory
cd - : go to the last directory you were in
cd .. : go up a directory cat : print file contents to the screen

cat filename.txt : cat the contents of filename.txt to your screen

tail : like cat, but only reads the end of the file
tail /var/log/messages : see the last 20 (by default) lines of /var/log/messages
tail -f /var/log/messages : watch the file continuously, while it's being updated
tail -200 /var/log/messages : print the last 200 lines of the file to the screen

more : like cat, but opens the file one screen at a time rather than all at once
more /etc/userdomains : browse through the userdomains file. hit Spaceto go to the next page, q to quit

pico : friendly, easy to use file editor
pico /home/burst/public_html/index.html : edit the index page for the user's website.

vi : another editor, tons of features, harder to use at first than pico
vi /home/burst/public_html/index.html : edit the index page for the user's website.

grep : looks for patterns in files
grep root /etc/passwd : shows all matches of root in /etc/passwd
grep -v root /etc/passwd : shows all lines that do not match root

touch : create an empty file
touch /home/burst/public_html/404.html : create an empty file called 404.html in the directory /home/burst/public_html/

ln : create's "links" between files and directories
ln -s /usr/local/apache/conf/httpd.conf /etc/httpd.conf : Now you can edit /etc/httpd.conf rather than the original. changes will affect the orginal, however you can delete the link and it will not delete the original.

rm : delete a file
rm filename.txt : deletes filename.txt, will more than likely ask if you really want to delete it
rm -f filename.txt : deletes filename.txt, will not ask for confirmation before deleting.
rm -rf tmp/ : recursively deletes the directory tmp, and all files in it, including subdirectories. BE VERY CAREFULL WITH THIS COMMAND!!!

last : shows who logged in and when
last -20 : shows only the last 20 logins
last -20 -a : shows last 20 logins, with the hostname in the last field

w : shows who is currently logged in and where they are logged in from.

netstat : shows all current network connections.
netstat -an : shows all connections to the server, the source and destination ips and ports.
netstat -rn : shows routing table for all ips bound to the server.

top : shows live system processes in a nice table, memory information, uptime and other useful info. This is excellent for managing your system processes, resources and ensure everything is working fine and your server isn't bogged down.
top then type Shift + M to sort by memory usage or Shift + P to sort by CPU usage

ps: ps is short for process status, which is similar to the top command. It's used to show currently running processes and their PID.
A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).
ps U username : shows processes for a certain user
ps aux : shows all system processes
ps aux --forest : shows all system processes like the above but organizes in a hierarchy that's very useful!

file : attempts to guess what type of file a file is by looking at it's content.
file * : prints out a list of all files/directories in a directory

du : shows disk usage.
du -sh : shows a summary, in human-readble form, of total disk space used in the current directory, including subdirectories.
du -sh * : same thing, but for each file and directory. helpful when finding large files taking up space.

wc : word count
wc -l filename.txt : tells how many lines are in filename.txt

cp : copy a file
cp filename filename.backup : copies filename to filename.backup
cp -a /home/burst/new_design/* /home/burst/public_html/ : copies all files, retaining permissions form one directory to another.

kill: terminate a system process
kill -9 PID EG: kill -9 431
kill PID EG: kill 10550
Use top or ps ux to get system PIDs (Process IDs)

EG:
PID TTY TIME COMMAND
10550 pts/3 0:01 /bin/csh

10574 pts/4 0:02 /bin/csh

10590 pts/4 0:09 APP

Each line represents one process, with a process being loosely defined as a running instance of a program. The column headed PID (process ID) shows the assigned process numbers of the processes. The heading COMMAND shows the location of the executed process.

Putting commands together

Often you will find you need to use different commands on the same line. Here are some examples. Note that the | character is called a pipe, it takes date from one program and pipes it to another.

> means create a new file, overwriting any content already there.
>> means tp append data to a file, creating a newone if it doesn not already exist.
< send input from a file back into a command.

grep User /usr/local/apache/conf/httpd.conf |more

This will dump all lines that match User from the httpd.conf, then print the results to your screen one page at a time.

last -a > /root/lastlogins.tmp

This will print all the current login history to a file called lastlogins.tmp in /root/

tail -10000 /var/log/exim_mainlog |grep domain.com |more

This will grab the last 10,000 lines from /var/log/exim_mainlog, find all occurances of domain.com (the period represents 'anything', -- comment it out with a so it will be interpretted literally), then send it to your screen page by page.

netstat -an |grep :80 |wc -l

Show how many active connections there are to apache (httpd runs on port 80)

mysqladmin processlist |wc -l

Show how many current open connections there are to mysql

Ref: http://forums.linuxwebadmin.info/index.php/topic,14.0.html

How to find which versions are required while upgrading your kernel / OS

How to find a version some tools which are required while upgrading your kernel / OS:

How to find a version some tools which are required while upgrading your kernel / OS

     Name:             How to find version:

     Gnu C Compiler     gcc --version
     Gnu Make           make --version
     binutils           ld -v
     util-linux         fdformat --version
     module-init-tools  depmod -V
     procps             ps --version
     [procps 2.x] [procps 3.x]

     e2fsprogs          tune2fs
     jfsutils           fsck.jfs -V
     reiserfsprogs      reiserfsck -V 2>&1 | grep reiserfsprogs
     xfsprogs           xfs_db -V
     nfs-utils          showmount --version
     pcmcia-cs          cardmgr -V
     quota-tools        quota -V
     PPP                ppd --version
     isdn4k-utils       isdnctrl 2>&1 | grep version
     oprofile           oprofiled --version