notes update

src/rhcsa.md

@@ -1365,4 +1365,175 @@ awk -F: '{print $NF}' file.txt # print the last field separated by a colon
 sed 's/old/new/' file.txt # replace old with new
 
 sed 's/old/new/g' file.txt # replace all instances of old with new
+
+sed -n '1p' file.txt # print the first line and suppress the rest of the output
+
+sed -i 's/old/new/g' file.txt # replace all instances of old with new in the file
+```
+
+## Manage Files and Directories
+
+### Listing Directory Content
+```bash
+ls # list the directory content
+
+ls -l # list the directory content in long format
+
+ls -a # list the directory content including hidden files
+```
+
+### Making Directories
+```bash
+mkdir test # make a new directory
+
+mkdir -p test/test2 # make a new directory and all the necessary parent directories
+```
+
+### Traversing the File System
+```bash
+cd # change to the home directory
+
+cd ~ # change to the home directory
+
+cd .. # change to the parent directory
+```
+
+### Creating and Opening Files
+```bash
+touch file.txt # create a new file
+
+cat > file.txt # create a new file and write to it
+
+cat file.txt # display the contents of the file
+```
+
+### Removing Files and Directories
+```bash
+rm file.txt # remove a file
+
+rm -r test # remove a directory and all its contents
+
+rm -f file.txt # remove a file without asking for confirmation
+```
+
+### Copying and Moving
+```bash
+cp file.txt file_copy.txt # copy a file
+
+cp -r test test_copy # copy a directory and all its contents
+
+mv file.txt file_copy.txt # move a file
+```
+
+## Understand and Modify File Permissions
+
+### Understanding Owners, Groups & Others
+```bash
+### ugo
+u # user
+g # group
+o # others
+
+### rwx
+r # read
+w # write
+x # execute
+
+### numeric notation
+1 # execute
+2 # write
+4 # read
+5 # read and execute
+6 # read and write
+7 # read, write and execute
+
+### breakdown of permissions
+-rw-r--r--. 1 hugh hugh 0 Mar 12 09:53 file1.txt
+
+-rw- # user has read and write permissions
+r-- # group has read permissions
+r-- # others have read permissions
+
+### id
+id # display the user's id
+
+id -u # display the user's id
+
+id -g # display the user's group id
+```
+
+### Changing Ownership
+```bash
+chown user:group file.txt # change the owner and group of the file
+
+chown user file.txt # change the owner of the file
+
+chown :group file.txt # change the group of the file
+```
+
+### Symbolic Notation
+```bash
+chmod u+x file.txt # add execute permission to the user
+
+chmod u-x file.txt # remove execute permission from the user
+
+chmod u+x,g+w file.txt # add execute and write permissions to the user and group
+```
+
+### Octal Notation
+```bash
+chmod 755 file.txt # change the permissions of the file to read, write and execute for the user and read and execute for the group and others
+
+chmod 644 file.txt # change the permissions of the file to read and write for the user and read for the group and others
+```
+
+### Special Permissions
+```bash
+### sticky bit is used to prevent users from deleting or renaming files in a directory
+### symbolic notation
+chmod +t file.txt # add the sticky bit to the file
+chmod -t file.txt # remove the sticky bit from the file
+chmod +t directory/ # add the sticky bit to the directory
+### octal notation
+chmod 1755 file.txt # add the sticky bit to the file
+chmod 0755 file.txt # remove the sticky bit from the file
+chmod 1755 directory/ # add the sticky bit to the directory
+
+### SUID is used to set the user id on a file
+### symbolic notation
+chmod u+s file.txt # add the SUID to the file
+chmod u-s file.txt # remove the SUID from the file
+chmod u+s directory/ # add the SUID to the directory
+### octal notation
+chmod 4755 file.txt # add the SUID to the file
+chmod 0755 file.txt # remove the SUID from the file
+chmod 4755 directory/ # add the SUID to the directory
+
+
+### symbolic notation
+### SGID is used to set the group id on a file
+chmod g+s directory/ # add the SGID to the directory
+
+### octal notation
+chmod 2755 file.txt # add the SGID to the file
+chmod 0755 file.txt # remove the SGID from the filechmod g-s file.txt # remove the SGID from the file
+
+### -rwSr--r--. vs -rwsr--r--.
+-rwSr--r--. # file is not executable
+-rwsr--r--. # file is executable and has the SUID set
+
+### to fix this
+chmod u+x file.txt # add the execute permission to the user
+chmod u+s file.txt # add the SUID to the file
+
+chmod 4755 file.txt # add the SUID to the file
+```
+
+### Configuring Default Permissions
+```bash
+umask # display the current umask
+
+umask 022 # set the umask to 022
+
+umask 000 # set the umask to 000
 ```