Useful Linux Scripts · Wouter Dullaert

This article originally appeared on http://olezfdtd.wordpress.com I’ve copied it over to my current blog to consolidate all my blogging efforts over the years in one place.

We didn’t come up with this one, but it’s a very handy reference guide. In good medieval monastery style, we’re copying it here in order to safeguard this information for future generations.

PS command:

The PS command is useful to check for performance problems:

Displaying top CPU-consuming processes:

ps aux | head -1; ps aux | sort -rn +2 | head -10

Displaying top 10 memory-consuming processes:

ps aux | head -1; ps aux | sort -rn +3 | head

Displaying process in order of being penalized:
```
ps -eakl | head -1; ps -eakl | sort -rn +5
```
Displaying process in order of priority:
```
ps -eakl | sort -n +6 | head
```
Displaying process in order of nice value
```
ps -eakl | sort -n +7
```

Displaying the process in order of time

ps vx | head -1;ps vx | grep -v PID | sort -rn +3 | head -10

Displaying the process in order of real memory use

ps vx | head -1; ps vx | grep -v PID | sort -rn +6 | head -10

Displaying the process in order of I/O

ps vx | head -1; ps vx | grep -v PID | sort -rn +4 | head -10

Displaying WLM classes

ps -a -o pid, user, class, pcpu, pmem, args

Determinimg process ID of wait processes:
```
ps vg | head -1; ps vg | grep -w wait
```
Wait process bound to CPU (replace PID with the actual process number)
```
ps -mo THREAD -p PID
```

lsof Command

List all open files:
```
lsof
```
List all open Internet, x.25 (HP-UX), and UNIX domain files:
```
lsof -i -U
```
List all open IPv4 network files in use by the process whose PID is 1234:
```
lsof -i 4 -a -p 1234
```
List all files using any protocol on ports 513, 514, or 515 of host wonderland.cc.purdue.edu:
```
lsof -i @wonderland.cc.purdue.edu:513-515
```
List all files using any protocol on any port of mace.cc.purdue.edu (cc.purdue.edu is the default domain)::
```
lsof -i @mace
```
List all open files for login name “abe”, or user ID 1234, or process 456, or process 123, or process 789:
```
lsof -p 456,123,789 -u 1234,abe
```
List all open files on device /dev/hd4:
```
lsof /dev/hd4
```
Find the process that has /u/abe/foo open:
```
lsof /u/abe/foo
```
Send a SIGHUP to the processes that have /u/abe/bar open:
```
kill -HUP `lsof -t /u/abe/bar`
```
Find any open file, including an open UNIX domain socket file, with the name /dev/log:
```
lsof /dev/log
```
Find processes with open files on the NFS file system named /nfs/mount/point whose server is inaccessible, and presuming your mount table supplies the device number for /nfs/mount/point:
```
lsof -b /nfs/mount/point
```
Do the preceding search with warning messages suppressed:
```
lsof -bw /nfs/mount/point
```
Ignore the device cache file:
```
lsof -Di
```
Obtain PID and command name field output for each process, file descriptor, file device number, and file inode number for each file of each process:
```
lsof -FpcfDi
```
List the files at descriptors 1 and 3 of every process running the lsof command for login ID “abe” every 10 seconds:
```
lsof -c lsof -a -d 1 -d 3 -u abe -r10
```
List the current working directory of processes running a command that is exactly four characters long and has an o or O in character three with this regular expression form of the -c c option:
```
lsof -c /^..o.$/i -a -d cwd
```
Find an IP version 4 socket file by its associated numeric dot-form address:
```
lsof [email protected]
```
Display list of open ports:
```
lsof -i
```
List information about TCP sessions on your server (specifically SSH in this example):
```
lsof -i tcp@`hostname`:22
```
List information about all TCP session:
```
lsof -i tcp@`hostname`
```
List information about all sockets using port 53 (will display named information on UDP/TCP)
```
lsof -i @`hostname`:53
```
List information about all UDP sessions
```
lsof -i udp@`hostname`
```
List all open files with “ssh” in them:
```
lsof -c ssh
```
List everything but with UIDs insted of the UID name from /etc/passwd:
```
lsof -l
```
List all open files with “ssh” and only the UIDs:
```
lsof -l -c ssh
```
List all open files for the /tmp dir. Very slow, but good for finding that nasty process that’s holding a file open (although: fuser -m /tmp, will do the same thing):
```
lsof+D /tmp
```

fuser and netstat Commands

Kill all processes accessing the file system /home in any way:
```
fuser -km /home
```
Invoke something if no other process is using /dev/ttyS1:
```
if fuser -s /dev/ttyS1; then :; else something; fi
```

Some Important Command to find DDOS Attack:

fuser telnet/tcp shows all processes at the (local) TELNET port.

netstat -anp |grep 'tcp\|udp' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n

netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr

netstat -ntu | grep -v TIME_WAIT | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr

bash netstat -an | grep :80 | awk '{print $5}' | cut -f1 -d":" | sort | uniq -c | sort -n`

netstat command example:
```
netstat –listen
```
Display open ports and established TCP connections:
```
netstat -vatn
```
For UDP port try following command:
```
netstat -vaun
```
If you want to see FQDN then remove -n flag:
```
netstat -vat
```

Menu

PS command:

lsof Command

fuser and netstat Commands