I need to find and list all hidden files including directories on a Linux server (CentOS). How can I recursively list all hidden files and directories? How do I save result in a text file? And How do I delete all hidden files/directories ?

Using the find command to list all hidden files recursively

# find  -name ".*" -print

Example

# find /etc/ -name ".*" -print
/etc/skel/.bashrc
/etc/skel/.bash_logout
/etc/skel/.bash_profile
/etc/.pwd.lock

Or,

# find  -name ".*" -ls

Example

# find /etc/ -name ".*" -ls
1310797    4 -rw-r--r--   1 root     root          124 May 11  2012 /etc/skel/.bashrc
1310794    4 -rw-r--r--   1 root     root           18 May 11  2012 /etc/skel/.bash_logout
1310796    4 -rw-r--r--   1 root     root          176 May 11  2012 /etc/skel/.bash_profile
1310854    0 -rw-------   1 root     root            0 Dec 12  2012 /etc/.pwd.lock

If you only want to search only hidden files:

# find  -type f -iname ".*" -ls

Example

# find /usr -type f -iname ".*" -ls
8915163    4 -rw-r--r--   1 root     root          760 Sep 19  2012 /usr/share/man/man5/.k5login.5.gz
8651596    4 -rw-r--r--   1 root     root           40 May 11  2012 /usr/share/man/man1/..1.gz
8654188    4 -rw-r--r--   1 root     root         2438 Aug 25 14:29 /usr/local/lib/php/.depdb
8654187    0 -rw-r--r--   1 root     root            0 Aug 25 14:29 /usr/local/lib/php/.depdblock
8654186    0 -rw-r--r--   1 root     root            0 Aug 25 14:29 /usr/local/lib/php/.lock
...

Or, If you only want to search only hidden directories:

find  -type d -iname ".*" -ls

Example

# find /usr -type d -iname ".*" -ls
8654180    4 drwxr-xr-x   3 root     root         4096 Dec 12  2012 /usr/local/lib/php/.channels
8785283    4 drwxr-xr-x   2 root     root         4096 Dec 12  2012 /usr/local/lib/php/.channels/.alias
8654179    4 drwxr-xr-x   5 root     root         4096 Dec 12  2012 /usr/local/lib/php/.registry
...

To remove all hidden files recursively

# find  -type f -iname ".*" -print0 | xargs -0 rm -f

Example

# Delete all hidden files of apache server
# find /var/www/html -type f -iname ".*" -print0 | xargs -0 rm -f

The post Centos: How To List All / Delete Hidden Files Recursively ? appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

An ISO image (International Organization for Standardization) is an archive file (also known as a disc image) of an optical disc, composed of the data contents of every written sector of an optical disc, including the optical disc file system. ISO images can be created from optical discs, or can be used to recreate optical discs using software from many software vendors. ISO image files typically have a file extension of .iso. The name ISO is taken from the ISO 9660 file system used with CD-ROM media, but an ISO image might also contain a UDF (ISO/IEC 13346) file system.

To mount an ISO image under Linux, you need simply to do the following steps.

Step 1. You must be logged in as root. If not root user then switch to root user using following command:

$ sudo -i

If you are using RedHat / CentOS / Fedora

$ su

Step 2. Create a mounpoint, example /mnt/iso

# mkdir -p /mnt/iso

Step 3. Use mount command as follows to mount iso file called image.iso

# mount -o loop image.iso /mnt/iso

Where,
-o: Options are specified with a -o flag followed by a comma separated string of options. Some of these options are only useful when they appear in the /etc/fstab file. (More)

loop: A loop device is a pseudo-device that makes a file accessible as a block device. Loop devices are often used for CD ISO images and floppy disc images. Mounting a file containing a filesystem via such a loop mount makes the files within that filesystem accessible. They appear in the mount point directory using above commands.

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If you store private information on your Linux system and you want to prevent other people who use the system from viewing your private files, you need to password protect these files. Solution is to use following commands to encrypt or decrypt files with a password.

gpg command

GnuPG is the GNU project’s complete and free implementation of the OpenPGP standard as defined by RFC4880. GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.

To encrypt a file, use command gpg as follows:

$ gpg -c filename

Example, to encrypt private.txt file, type the command

$ gpg -c private.txt

Output

Enter passphrase:
Repeat passphrase:

Where,
-c : Encrypt with symmetric cipher.

To decrypt file use gpg command

$ gpg private.txt.gpg

Output:

gpg private.txt.gpg
gpg: CAST5 encrypted data
Enter passphrase:

mcrypt command

Mcrypt is a simple crypting program, a replacement for the old unix crypt. When encrypting or decrypting a file, a new file is created with the extension .nc and mode 0600. The new file keeps the modification date of the original. The original file may be deleted by specifying the -u parameter.

Examples, to encrypt data.txt file, type the following command

$ mcrypt data.txt

Output:

Enter the passphrase (maximum of 512 characters)
Please use a combination of upper and lower case letters and numbers.
Enter passphrase:
Enter passphrase:

Note that a new file is created with the extension .nc.

To decrypt the data.txt.nc file, enter

$ mcrypt -d data.txt.nc

Output:

Enter passphrase:
File data.txt.nc was decrypted.

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While having a large hard drive is good for storing lots of data, it is also important for your computer to have a fast hard drive. Faster hard drives help your computer run more smoothly. You can use the hdparm tool or dd command to determine your disk speeds from the Linux command line.

List Hard Drives

Open a terminal or go to a command line on your Linux system. As root, run the command:

[root@server2 ~]# fdisk -l

Sample outputs:

Disk /dev/sda: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14         274     2096482+  83  Linux
/dev/sda3             275         535     2096482+  82  Linux swap / Solaris
/dev/sda4             536       30400   239890612+   5  Extended
/dev/sda5             536       30400   239890581   83  Linux

Disk /dev/sdb: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          13      104391   83  Linux
/dev/sdb2              14         274     2096482+  83  Linux
/dev/sdb3             275         535     2096482+  82  Linux swap / Solaris
/dev/sdb4             536       30400   239890612+   5  Extended
/dev/sdb5             536       30400   239890581   83  Linux

hdparm command

You can use the hdparm command to check hard disk speed. It provides a command line interface to various hard disk ioctls supported by the stock Linux ATA/IDE/SATA device driver subsystem. Login as the root and enter the following command:

[root@server2 ~]# hdparm -tT /dev/sda

Sample outputs:

/dev/sda:
 Timing cached reads:   29084 MB in  2.00 seconds = 14574.71 MB/sec
 Timing buffered disk reads:  308 MB in  3.01 seconds = 102.36 MB/sec

Note:
-t :perform device read timings
-T :perform cache read timings
/dev/sda : Hard disk device file

dd Command

You can use the dd command as follows to get speed info too:

[root@server2 ~]# dd if=/dev/zero of=/tmp/test.img bs=8k count=256k
[root@server2 ~]# rm /tmp/test.img

Sample outputs:

dd: writing `/tmp/test.img': No space left on device
210779+0 records in
210778+0 records out
1726697472 bytes (1.7 GB) copied, 22.3398 seconds, 77.3 MB/s

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What are the SUID, SGID and the Sticky Bits?

Sticky Bit

Lets start with Sticky bit first. Since this is the most simplest to explain. Setting the sticky bit tells Unix that once the concerned application is executed, it should remain in memory. Remember that Unix is a multi-user OS and was mainly designed so that multiple users can work simultaneously. Thus the logic used is that a program that exists in memory requires lesser time to start when a new user requests for the same program. Thus when one user has just used a program and then a new user wants to use the same program, the second user doesn’t have to face a time delay for the program to initialize itself. It would be readily available to him. The concept of the sticky bit was a very useful one, long back when fast disk access and other memory access technologies weren’t around. But in today’s age the concept of sticky bit is obsolete, since modern day technology is advanced enough to reduce the time delay while loading applications into the memory. Thus currently the sticky bit is of very little significance. Sticky bit is only associated with executables.

SUID (Set User ID) Bit

Sometime you may faced an error while trying to run any application stating that the application must be ‘SUID root’ . You might have been confused that time, but now once you read this article you would no longer find it confusing.

SUID stands for Set User ID. This means that if the SUID bit is set for any application then your user ID would be set as that of the owner of application/file rather than the current user, while running that application. That means in case I have an application whose owner is ‘ root ‘ and it has its SUID bit set, then when I run this application as a normal user, that application would still run as root. Since the SUID bit tells Linux that the the User ID root is set for this application and whenever this application executes it must execute as if root was executing it (since root owns this file).

SGID (Set Group ID) bit

Just like SUID, setting the SGID bit for a file sets your group ID to the file’s group while the file is executing. IT is really useful in case you have a real multi-user setup where users access each others files. As a single homeuser I haven’t really found a lot of use for SGID. But the basic concept is the same as the SUID, the files whose SGID bit are set would be used as if they belong to that group rather than to that user alone.

Setting the SUID/SGID bits

Setting SUID bits on the file:
Suppose I got the executable called “killprocess” and I need to set the suid bit on this file, go to command prompt and issue command:

chmod u+s filename

Now check permission on the file with command

ls -l filename

Observe “s” that has been added for suid bit

-rwsr-xr-x 1 root root 8 Jun  8 10:10 filename

Setting GUID bits on the file:
Go to command prompt and issue command:

chmod g+s filename

This will set the GUID bit on the same file, check the permission on this file using command:

ls -l filename

-rwsr-sr-x 1 root root 8 Jun  8 12:11 filename

Setting Sticky bits on the folder:

chmod +t folder

Find SUID/SGID files

Find all SUID root files:

find / -user root -perm -4000 -print

Find all SGID root files:

find / -group root -perm -2000 -print

Find all SUID and SGID files owned by anyone:

find / -perm -4000 -o -perm -2000 -print

The post SUID, SGID and Sticky Bits appeared first on lifeLinux: Linux Tips, Hacks, Tutorials, Ebooks.

Q. Is there an easy way to recursively copy all files include hidden files in a directory to another directory?

A. Using rsync command is a better solution.

rsync -av --progress /source /destination

With:

-a: Archive Mode

-v: Verbose Mode

–progress: Show progress during transfer.

Another solution, you may also use cp command and pattern matches, type the following command:

cp -R ./[^.]* /destination

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If you want to delete all data contained in your hard drive so that you render it empty in case you want to sell it or for any other reasons, you need to follow these steps:

1. Turn on your computer and boot from Debian Live CD or any of its variants (Debian, Ubuntu, Xubuntu, Edubuntu, Ubuntulite, Fluxbuntu, etc.).
2. In the terminal, run the command given below to disable the swap partition:

sudo swapoff

Note: If you don’t execute this command, some data might remain on your hard drive.

3. Now you have to run the command listed below to zero out your hard drive:

sudo dd if=/dev/zero of=/dev/sda

The formatting process might take a long time to finish, this depends on the size of your hard disk. To view remaining time, you have to run this command:

sudo killall -USR1 dd

Upon running the command listed above, you will be shown the disk space “cleaned” in GB.

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