Linux Misc

May 16, 2017 (updated: May 24, 2017)

1. 1. Linux distribution info
2. 2. Check ram info
3. 3. Shell
   1. 3.1. File operators
   2. 3.2. String operators
   3. 3.3. Number operators
   4. 3.4. Script environment

Open files

Network Usage

1. 1. Password
   1. 1.1. random password
   2. 1.2. nginx basic auth

Linux distribution info

• cat /etc/*-release
• lsb_release -a
• uname -mrs

Check ram info

• sudo dmidecode -t memory
• sudo lshw -short -C memory

Shell

File operators

operator	description
-e	file exists
-a	same as -e, deprecated
-f	file is a regular file (not a directory or device file)
-s	file is not zero size
-d	file is a directory
-b	file is a block device
-c	file is a character device
-p	file is a pipe
-h	file is a symbolic link
-L	file is a symbolic link
-S	file is a socket
-t	file is associated with a terminal device
-r	file has read permission
-w	file has write permission
-x	file has execution permission
-O	you are owner of file
-G	group-id of file same as yours
-N	file modified since it was last read
f1 -nt f2	file f1 is newer than f2
f1 -ot f2	file f1 is older than f2
f1 -ef f2	files f1 and f2 are hard links to the same file

String operators

operator	description
-n	the length is nonzero
-z	the length is zero
s1 = s2	two strings are identical
s1 != s2	two strings are not identical
s1	s1 is not null

Number operators

operator	description
-eq	equal
-ne	not equal
-gt	greater than
-ge	greater or equal
-lt	less than
-le	less or equal

Script environment

• set -x Print commands and their arguments as they are executed.
• set +x Disabling it.

Open files

List File Opened By a PID

sudo lsof -p <pid>

List File Descriptors in Kernel Memory

sudo sysctl fs.file-max

Network Usage

sudo apt-get install speedometer

Password

random password

openssl rand -base64 12

nginx basic auth

location /protected {
    autoindex on;
    auth_basic "Restricted";
    auth_basic_user_file /etc/nginx/conf.d/.htpasswd;
}

echo "user:$(openssl passwd -1 password)\n" >> .htpasswd