Overview of the transport layer: the relationship between ports and processes

Bash scripts handle command line parameters through special variables. Use $1, $2, etc. to get positional parameters, where $0 represents the script name; iterates through "$@" or "$*", the former retains space separation, and the latter is merged into a single string; use getopts to parse options with parameters (such as -a, -b:value), where the option is added to indicate the parameter value; at the same time, pay attention to referring to variables, using shift to move the parameter list, and obtaining the total number of parameters through $#.

The shutdown command of Linux/macOS can be shut down, restarted, and timed operations through parameters. 1. Turn off the machine immediately and use sudoshutdownnow or -h/-P parameters; 2. Use the time or specific time point for the shutdown, cancel the use of -c; 3. Use the -r parameters to restart, support timed restart; 4. Pay attention to the need for sudo permissions, be cautious in remote operation, and avoid data loss.

There are three main ways to add a new APT repository: use the add-apt-repository command to be suitable for common PPAs or officially supported repositories; manually create .list files suitable for fine control or non-supporting the former repository; use .deb lines to write source files directly to specific statements provided by the official website. You also need to pay attention to updating the source list and adding GPG keys to ensure security.

The steps to configure an NTP server include installing services, modifying configuration files, checking synchronization status, and setting up a firewall. 1. Install NTP service: Use sudoapt on Ubuntu/Debian, use sudoyum to install on CentOS/RHEL, start and enable the service after installation; 2. Modify the configuration file /etc/ntp.conf: Add trusted upstream servers such as serverntp.aliyun.comiburst and servertime.windows.comiburst, and set allow access to network segments such as restrict192.168.1.0mask255.255.255.0nomod

To set a group disk quota, 1. Confirm the file system to support and enable the mount option; 2. Remount or restart to make the configuration take effect; 3. Initialize the quota database; 4. Use edquota or xfs_quota to set group restrictions; 5. Enable quota and check the usage regularly. Specific operations include editing /etc/fstab to add usrquota, grpquota parameters, using quotacheck or xfs_quota to generate database files, setting soft and hard limits through edquota-g, running quotaon to enable quota, and viewing reports through repquota or xfs_quota. It is recommended to configure timed tasks to monitor quota status.

If you want to know the network connection on your current computer, you can view it through the command line tool; use netstat-ano on Windows to view all connections and PIDs, use ss-tulnp and lsof-i-P to obtain detailed information, and can also be monitored in real time through graphical interface tools such as resource monitor, nethogs, etc.

To create an LVM volume group, you must first prepare a physical volume (PV) and then create a VG. 1. Use pvcreate to initialize the hard disk or partition into PV, such as pvcreate/dev/sdb1; 2. Use the vgcreate command to combine one or more PVs into VG, such as vgcreatemy_volume_group/dev/sdb1/dev/sdc1; 3. You can customize the PE size through the -s parameter and use vgdisplay to view information; 4. You can dynamically expand VG in the future and add a new PV using vgextend; 5. Before deleting VG, you must confirm that there is no LV and delete it with vgremove.

The steps to configure an NFS server are as follows: 1. Install the nfs-utils or nfs-kernel-server package; 2. Start and enable nfs-server and related RPC services; 3. Edit /etc/exports to configure shared directories and permissions, such as rw, ro, sync, etc.; 4. Execute exportfs-a and open the firewall port; 5. The client uses the mount command to mount or configure fstab to achieve automatic mount; Common problems include permission control, ID mapping, RPC service not being started and configuration not being refreshed, and needs to be checked in conjunction with logs.