背景

最近遇到个两年前遇到的问题，使用virt-manager提示(virt-manager:873): Gtk-WARNING **: 14:53:28.147: cannot open display: :1，当时专门运维的同事帮忙临时调了下DISPLAY变量，好像是将:1改成了SSH用户本地IP:10.0，当时的确好了，用完就关了再没用到，也没深究原因，那个运维同事也不大理解(网上查到的解决办法)。然而最近在做资产盘点，领导让我把我挂名管理的服务器作置换申请，需要知道虚拟机的信息，赶上盘到两年前有问题的机器上，又出现同样的问题，经过查找了资料找到了个几乎万无一失的理解，记一记.

DISPLAY变量是啥

首先，它是Linux X11 server（显示服务）用到的一个环境变量，用来指示你的显示(也可以包含键盘和鼠标)指向的显示服务地址，通常桌面PC该值会被设为:0.0 .

其次，它的格式有三部分： [主机名]:显示服务端口号-6000.显示器编号 。

• [主机名] ：一般是可以省略的，可以不写，也可以写成$HOSTNAME变量表示的主机名 或 localhost
• 显示服务端口号-6000：意思是sshd服务的X11Forwarding占用端口减去6000的值
• 显示器编号：一般都是0，表示第一个显示器

如何正确设置DISPLAY变量

分两种情况:

• Linux桌面系统：直接设置:0.0
• SSH连接的Linux服务器：需要按照格式进行检查。

检查步骤如下:

[root@hz ~]# netstat -anpt |grep sshd |grep LISTEN |grep 60
tcp   0  0 127.0.0.1:6010  0.0.0.0:*  LISTEN   30346/sshd: root@pt
tcp6  0  0 ::1:6010        :::*       LISTEN   30346/sshd: root@pt

找到60开头的sshd端口，这时是6010，减去6000是10，SSH只写第一显示器编号 。

则我的DISPLAY变量可设为 :10.0 或者 hz:10.0 。

如果上边的命令查不出来6000左右的端口号，请检查 /etc/ssh/sshd_config，确认X11Forwarding yes参数已配置并systemctl restart sshd，使用exit退出当前ssh，重新连接再尝试.

附：参考

The magic word in the X window system is DISPLAY. A display consists (simplified) of

• a keyboard,
• a mouse
• and a screen.

A display is managed by a server program, known as an X server. The server serves displaying capabilities to other programs that connect to it. 。

The remote server knows where it has to redirect the X network traffic via the definition of the DISPLAY environment variable which generally points to an X Display server located on your local computer. 。

The value of the display environment variable is

hostname:D.S

where

hostname is the name of the computer where the X server runs. An omitted hostname means the localhost. 。

D is a sequence number (usually 0). It can be varied if there are multiple displays connected to one computer. 。

S is the screen number. A display can actually have multiple screens. Usually, there's only one screen though where 0 is the default. 。

Example of values 。

localhost:4
google.com:0
:0.0

hostname:D.S means screen S on display D of host hostname; the X server for this display is listening at TCP port 6000+D. 。

host/unix:D.S means screen S on display D of host host; the X server for this display is listening at UNIX domain socket /tmp/.X11-unix/XD (so it's only reachable from host). 。

:D.S is equivalent to host/unix:D.S, where host is the local hostname. 。

:0.0 means that we are talking about the first screen attached to your first display in your local host 。

Read more here: support.objectplanet.com and here: superuser.com and here: docstore.mik.ua. 。

From a X(7) man page

From the user's perspective, every X server has a display name of the form

hostname:displaynumber.screennumber 。

This information is used by the application to determine how it should connect to the server and which screen it should use by default (on displays with multiple monitors)

hostname The hostname specifies the name of the machine to which the display is physically connected. If the hostname is not given, the most efficient way of communicating to a server on the same machine will be used. displaynumber The phrase "display" is usually used to refer to a collection of monitors that share a common keyboard and pointer (mouse, tablet, etc.). Most workstations tend to only have one keyboard, and therefore, only one display. Larger, multi-user systems, however, frequently have several displays so that more than one person can be doing graphics work at once. To avoid confusion, each display on a machine is assigned a display number (beginning at 0) when the X server for that display is started. The display number must always be given in a display name. screennumber Some displays share a single keyboard and pointer among two or more monitors. Since each monitor has its own set of windows, each screen is assigned a screen number (beginning at 0) when the X server for that display is started. If the screen number is not given, screen 0 will be used. 。

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