Useful Linux Scripts
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:
1) Displaying top CPU-consuming processes:
ps aux | head -1; ps aux | sort -rn +2 | head -10
2) Displaying top 10 memory-consuming processes:
ps aux | head -1; ps aux | sort -rn +3 | head
3) Displaying process in order of being penalized:
ps -eakl | head -1; ps -eakl | sort -rn +5
4) Displaying process in order of priority:
ps -eakl | sort -n +6 | head
5) Displaying process in order of nice value
ps -eakl | sort -n +7
6) Displaying the process in order of time
ps vx | head -1;ps vx | grep -v PID | sort -rn +3 | head -10
7) Displaying the process in order of real memory use
ps vx | head -1; ps vx | grep -v PID | sort -rn +6 | head -10
8) Displaying the process in order of I/O
ps vx | head -1; ps vx | grep -v PID | sort -rn +4 | head -10
9) Displaying WLM classes
ps -a -o pid, user, class, pcpu, pmem, args
10) Determinimg process ID of wait processes:
ps vg | head -1; ps vg | grep -w wait
11) Wait process bound to CPU (replace PID with the actual process number)
ps -mo THREAD -p PID
lsof Command:
1) List all open files:
lsof
2) List all open Internet, x.25 (HP-UX), and UNIX domain files:
lsof -i -U
3) List all open IPv4 network files in use by the process whose PID is 1234:
lsof -i 4 -a -p 1234
4) 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
5) List all files using any protocol on any port of mace.cc.purdue.edu (cc.purdue.edu is the default domain)::
lsof -i @mace
6) 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
7) List all open files on device /dev/hd4:
lsof /dev/hd4
8) Find the process that has /u/abe/foo open:
lsof /u/abe/foo
9) Send a SIGHUP to the processes that have /u/abe/bar open:
kill -HUP `lsof -t /u/abe/bar`
10) Find any open file, including an open UNIX domain socket file, with the name /dev/log:
lsof /dev/log
11) 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
12) Do the preceding search with warning messages suppressed:
lsof -bw /nfs/mount/point
13) Ignore the device cache file:
lsof -Di
14) 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
15) 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
16) 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
17) Find an IP version 4 socket file by its associated numeric dot-form address:
lsof -i@128.210.15.17
18) Display list of open ports:
lsof -i
19) List information about TCP sessions on your server (specifically SSH in this example):
lsof -i tcp@`hostname`:22
20) List information about all TCP session:
lsof -i tcp@`hostname`
21) List information about all sockets using port 53 (will display named information on UDP/TCP)
lsof -i @`hostname`:53
22) List information about all UDP sessions
lsof -i udp@`hostname`
23) List all open files with “ssh” in them:
lsof -c ssh
24) List everything but with UIDs insted of the UID name from /etc/passwd:
lsof -l
25) List all open files with “ssh” and only the UIDs:
lsof -l -c ssh
26) 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:
1) Kill all processes accessing the file system /home in any way:
fuser -km /home
2) Invoke something if no other process is using /dev/ttyS1:
if fuser -s /dev/ttyS1; then :; else something; fi
3) 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
netstat -an | grep :80 | awk '{print $5}' | cut -f1 -d":" | sort | uniq -c | sort -n
4) netstat command example:
netstat –listen
5) Display open ports and established TCP connections:
netstat -vatn
6) For UDP port try following command:
netstat -vaun
7) If you want to see FQDN then remove -n flag:
# netstat -vat
IT snippets from phd-land 