Linux Commands
About Commands
Parameters and Flags
- A single hyphen (
-
) can be followed by multiple single-character flags. - A double hyphen (
--
) prefixes a single, multi-character option.
Consider this example:
tar -czf
In this example, -czf
specifies three single-character flags: c
, z
, and f
.
Now consider another example:
tar --exclude
In this case, --exclude
specifies a single, multi-character option named exclude
. The double hyphen disambiguates the command-line argument, ensuring that tar
interprets it as exclude rather than a combination of e
, x
, c
, l
, u
, d
, and e
.
Commands
chmod – Change Mode
The chmod command sets the permissions of files or directories.
chmod <options> <permissions> <file name>
sudo chmod -R 755 /var/www/my_website
See the Linux chmod page for more information.
chown – Change Ownership
Used to change the ownership of a file or directory to another user and or group.
sudo chown -R www-data: /path/to/directory
find – Find Files
Syntax:
find <starting path> <options> <file name>
Find a file starting at the /
path, non-case sensitive, for the name linux.odt
:
find / -iname linux.odt
See the Linux find page for more information.
getent – Get Entries
getent
is a Unix command that helps a user get entries in a number of important text files called databases. This includes the passwd
and group
databases which store user information – hence getent
is a common way to look up user details on Unix.
Example: Get all the entries of the /etc/passwd
file:
getent passwd
Outputs something like:
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
dwatts:x:34182:1500:Daniel Watts:/home/dwatts:/bin/bash
- For more info see: https://askubuntu.com/questions/725120/can-anybody-explain-output-of-getent-passwd-command
grep – Search File Content
grep
is a string and pattern matching utility that displays matching lines found in files, and can also work with piped output from other commands.
Find all instances of the string my string
in the files under the /path/to/search
directory:
grep -r "my string" /path/to/search
See the grep command page for more information.
ls – List
List the names and information about files and directories.
Passing the -la
flag lists ALL files and directories (including hidden files).
$ ls -la
total 40
drwxr-xr-x 7 root staff 224 Apr 27 10:41 .
drwxr-xr-x 7 root staff 224 Jan 22 15:48 ..
drwxr-xr-x 8 root staff 256 Jan 22 15:48 .svn
-rw-r--r-- 1 root staff 1897 Apr 27 10:41 email.php
-rw-r--r-- 1 root staff 2695 Jan 22 15:48 file_downloads.php
-rw-r--r-- 1 root staff 6373 Apr 28 09:35 handle_errors.php
-rw-r--r-- 1 root staff 1191 Jan 22 15:48 mime_types.php
ls -l Output Columns
1 - File Permissions
│ 2 - Number of hard links
│ │ 3 - Owner name
│ │ │ 4 - Group Name
│ │ │ │ 5 - File Size
│ │ │ │ │ 6 - Month of last modification
│ │ │ │ │ │ 7 - Day of last modification
│ │ │ │ │ │ │ 8 - Time of last modification
│ │ │ │ │ │ │ │ 9 - File or Directory Name
│ │ │ │ │ │ │ │ │
└───────── └ └──────────── └──── └─── └── └─ └──── └────────
-rw-r--r-- 1 squarem1admin staff 1897 Apr 27 10:41 email.php
mkdir – Make Directory
Use the -p
flag to also create the any parent directories.
mkdir -p /path/to/directory
nano – File Editor
Create a new file and open it for editing with nano:
nano /path/to/file.ext
Use control+z
to exit and save.
rm – Remove
Remove will remove a directory or a file.
Passing -r
will remove everything below (inside) the directory you are removing.
rm -r directory_to_remove
tail – Read the Tail of a File
The tail command reads a file, and outputs the last part of it (the “tail”).
umask – Mode Creation Mask
The umask command returns, or sets, the value of the system’s file mode creation mask.
Web Server Commands
Linux Host
Description | Command |
---|---|
Get the current operating system. | lsb_release -da |
Get the hostname of the current machine. | hostname |
Get the IP Address of the current machine. | hostname -I |
Get the FQDN of the current machine. | hostname -f |
MySQL Database Server
Description | Command |
---|---|
MySQL version | mysql -V |
Apache HTTP Server
Description | Commands |
---|---|
Apache server version | /usr/sbin/apache2ctl -v |
PHP
Resource Name | Command |
---|---|
PHP Version | php -v |
PHP Configs (php.ini) Location | php -i | grep php.ini |
PHP Location | which php |