Useful Linux Commands

Command to find files accessed in last 30 days. will find files that is accessed in last 30 days, under root folder.

# find / type f -atime -30 

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List contents of a folder along with contents of its subfolder. But it will traverse only to a depth of one. ie, it will not show the contents of subfolder's subfolder.

# ls * 

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To print the iptables rules along with line number.

# iptables -L --line-numbers 

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 To find a particular rule with rule number #; where # is the rule number you want to list 

# iptables -L OUTPUT --line-numbers | grep ^# 

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 Change permission only for folders 

# find . -type d -exec chmod 755 {} \;

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 List with 777 permission 

#find . -type d -perm 777 

-------------------------------------------------------------------------------------------------------------------------- To list all the processes listening to port 80

 # lsof -i TCP:80|awk {'print $2'}

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 To kill all the process listening to apache port 443/80 

# lsof -i TCP:443|awk {'print $2'} | xargs kill -9 

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 Recursively chmod only directories 

find . -type d -exec chmod 755 {} \; 

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 Recursively set the execute bit on every directory 

chmod -R a+X * The +X flag sets the execute bit on directories only 

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 Recursively chmod only files 

find . -type f -exec chmod 644 {} \;

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 Recursively chmod only PHP files (with extension .php) f

ind . -type f -name '*.php' -exec chmod 644 {} \; 

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 Find all files in /home/user/demo directory $ find /home/user/demo -print 

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 Now find all files in /home/user/demo directory with permission 777 

$ find /home/user/demo -perm 777 -print 

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 Next you need to apply chmod on all these files using -exec option: 

$ find /home/user/demo -perm 777 -print -exec chmod 755 {} \; 

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 Command to find files modified on July 12 

ll|grep dr|awk '{print $9}' > 123 for i in `cat 123`;do ls -ld $i;done|grep "Jul 12"

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 How to See the SSH password guesses First, find the PID of the listening SSH daemon process: 

# ps axuww | egrep 'PID|ssh' 

Now become root and attach to the running daemon with 

strace: # strace -f -e 'read,write' -p12345

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find / -xdev -ls |sort -nrk 7 |head

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Screen Command

Command to create screen:

# screen -S screen_name

To exit from screen:

Just close the shell without logout

To list all running screens:

# screen -ls

To login to a particular screen with screen name "xxxx.screen_name"

# screen -r xxxx.screen_name