Linux Screen：虚拟终端管理器详解

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"Linux Screen 是一个虚拟终端管理器，允许用户在一个物理终端上多路复用多个进程，支持创建和管理多个窗口，每个窗口都像独立的SSH或telnet连接。这个工具在Linux环境中非常实用，尤其对于需要同时处理多个任务或者保持会话持久性的用户。" **Linux Screen 知识点详解** 1. **什么是Linux Screen** Linux Screen是一个终端复用器，它允许多个全屏程序在同一物理终端上同时运行。用户可以通过简单的命令在不同的会话和窗口间切换，即使终端被意外断开，也能恢复之前的工作状态。 2. **基本概念** - **会话（Session）**: 一个Screen会话包含一组窗口，用户可以在一个会话中创建多个窗口来运行不同的命令或程序。 - **窗口（Window）**: 每个Screen窗口就像是一个独立的终端，可以运行单独的命令或应用程序。 3. **启动和使用Screen** - **启动Screen**: 通过命令 `screen` 可以启动一个新的Screen会话。 - **创建窗口**: 在Screen会话内，使用 `Ctrl+A + C` 创建新窗口。 - **切换窗口**: 使用 `Ctrl+A + 数字键` 或 `Ctrl+A + A` 交替在窗口间切换。 - **退出Screen**: 使用 `Ctrl+A + D` 断开会话但不关闭Screen，或者输入 `exit` 关闭当前窗口并结束会话。 4. **定制Screen** Screen的配置可以通过修改 `.screenrc` 文件进行，这包括定义快捷键、设置窗口名称等。用户可以根据自己的需求自定义命令行提示符、字体、颜色等。 5. **Session Management Commands** - **列出所有会话**: `screen -ls` 显示当前系统中的所有Screen会话。 - **重新连接会话**: `screen -r` 或 `screen -r [session_name]` 可以重新连接到已存在的会话。 - **分离和附加会话**: `Ctrl+A + D` 分离当前会话，`screen -r` 重新附加。 6. **复制和粘贴** Screen支持在窗口间的文本复制和粘贴，使用 `Ctrl+A + ]` 开始选择文本，再用 `Ctrl+A + [' 粘贴。 7. **子进程执行** Screen可以作为子进程的容器，方便管理和控制后台任务。 8. **键绑定** 用户可以自定义键绑定以执行特定的Screen命令，例如将某个组合键设置为创建新窗口或切换窗口。 9. **流量控制** Screen提供了一种方式来控制数据流，如暂停和恢复程序的输出，这对于查看大量滚动信息或在网络不稳定时很有帮助。 10. **Termcap** Termcap库用于处理不同终端的特性，Screen依赖Termcap来正确显示在不同终端上的信息。 11. **消息和日志** Screen支持发送消息到其他窗口，以及记录会话日志，这对于协作和故障排查很有帮助。 Linux Screen 是一个强大且灵活的工具，它极大地提高了用户在命令行环境下的工作效率，尤其是在需要管理多个任务和进程时。熟练掌握Screen的使用，能够使你在Linux环境下更加得心应手。

6 Screen User’s Manual

‘-h num’ Set the history scrollback buﬀer to be num lines high. Equivalent to the

defscrollback command (see Section 12.1 [Copy], page 65).

‘-i’ Cause the interrupt key (usually C-c) to interrupt the display immediately

when ﬂow control is on. This option is equivalent to the interrupt argument

to the defflow command (see Chapter 15 [Flow Control], page 77). Its use is

discouraged.

‘-l’

‘-ln’ Turn login mode on or oﬀ (for /etc/utmp updating). This option is equivalent

to the deflogin command (see Section 10.4 [Login], page 47).

‘-ls [match]’

‘-list [match]’

Do not start screen, but instead print a list of session identiﬁcation strings

(usually of the form pid.tty.host; see Section 8.5 [Session Name], page 37).

Sessions marked ‘detached’ can be resumed with screen -r. Those marked

‘attached’ are running and have a controlling terminal. If the session runs

in multiuser mode, it is marked ‘multi’. Sessions marked as ‘unreachable’

either live on a diﬀerent host or are dead. An unreachable session is considered

dead, when its name matches either the name of the local host, or the speciﬁed

parameter, if any. See the -r ﬂag for a description how to construct matches.

Sessions marked as ‘dead’ should be thoroughly checked and removed. Ask your

system administrator if you are not sure. Remove sessions with the ‘-wipe’

option.

‘-L’ Tell screen to turn on automatic output logging for the windows.

‘-Logfile "file"’

By default logﬁle name is "screenlog.0". You can set new logﬁle name with the

-Logfile option.

‘-m’ Tell screen to ignore the $STY environment variable. When this option is

used, a new session will always be created, regardless of whether screen is

being called from within another screen session or not. This ﬂag has a special

meaning in connection with the ‘-d’ option:

-d -m Start screen in detached mode. This creates a new session but

doesn’t attach to it. This is useful for system startup scripts.

-D -m This also starts screen in detached mode, but doesn’t fork a new

process. The command exits if the session terminates.

‘-O’ Select a more optimal output mode for your terminal rather than true VT100

emulation (only aﬀects auto-margin terminals without ‘LP’). This can also be

set in your .screenrc by specifying ‘OP’ in the termcap command.

‘-p name_or_number|-|=|+’

Preselect a window. This is useful when you want to reattach to a speciﬁc

window or you want to send a command via the ‘-X’ option to a speciﬁc window.

As with screen’s select command, ‘-’ selects the blank window. As a special

case for reattach, ‘=’ brings up the windowlist on the blank window, while a

Chapter 3: Invoking Screen 7

‘+’ will create new window. The command will not be executed if the speciﬁed

window could not be found.

‘-q’ Suppress printing of error messages. In combination with ‘-ls’ the exit value is

set as follows: 9 indicates a directory without sessions. 10 indicates a directory

with running but not attachable sessions. 11 (or more) indicates 1 (or more)

usable sessions. In combination with ‘-r’ the exit value is as follows: 10 indi-

cates that there is no session to resume. 12 (or more) indicates that there are

2 (or more) sessions to resume and you should specify which one to choose. In

all other cases ‘-q’ has no eﬀect.

‘-Q’ Some commands now can be queried from a remote session using this ﬂag, e.g.

’screen -Q windows’. The commands will send the response to the stdout of

the querying process. If there was an error in the command, then the querying

process will exit with a non-zero status.

The commands that can be queried now are: echo info lastmsg number select

time title windows

‘-r [pid.sessionname]’

‘-r sessionowner/[pid.sessionname]’

Resume a detached screen session. No other options (except combinations

with ‘-d’ or ‘-D’) may be speciﬁed, though the session name (see Section 8.5

[Session Name], page 37) may be needed to distinguish between multiple de-

tached screen sessions. The second form is used to connect to another user’s

screen session which runs in multiuser mode. This indicates that screen should

look for sessions in another user’s directory. This requires setuid-root.

‘-R’ resumes screen only when it’s unambiguous which one to attach, usually when

only one screen is detached. Otherwise lists available sessions.

‘-RR’ Resume the ﬁrst appropriate detached screen session. If successful, all other

command-line options are ignored. If no detached session exists, start a new

session using the speciﬁed options, just as if ‘-R’ had not been speciﬁed. This

option is set by default if screen is run as a login-shell (actually screen uses

‘-xRR’ in that case). For combinations with the ‘-D’/‘-d’ option see there.

‘-s program’

Set the default shell to be program. By default, screen uses the value of the

environment variable $SHELL, or /bin/sh if it is not deﬁned. This option is

equivalent to the shell command (see Section 6.4 [Shell], page 28). See also

there.

‘-S sessionname’

Set the name of the new session to sessionname. This option can be used to

specify a meaningful name for the session in place of the default tty.host suf-

ﬁx. This name identiﬁes the session for the screen -list and screen -r com-

mands. This option is equivalent to the sessionname command (see Section 8.5

[Session Name], page 37).

‘-t name’ Set the title (name) for the default shell or speciﬁed program. This option is

equivalent to the shelltitle command (see Section 6.4 [Shell], page 28).

4 Customizing Screen

You can modify the default settings for screen to ﬁt your tastes either through a personal

.screenrc ﬁle which contains commands to be executed at startup, or on the ﬂy using the

colon command.

4.1 The .screenrc ﬁle

When screen is invoked, it executes initialization commands from the ﬁles .screenrc in the

user’s home directory and /usr/local/etc/screenrc. These defaults can be overridden in

the following ways: For the global screenrc ﬁle screen searches for the environment variable

$SYSSCREENRC (this override feature may be disabled at compile-time). The user speciﬁc

screenrc ﬁle is searched for in $SCREENRC, then $HOME/.screenrc. The command line

option ‘-c’ speciﬁes which ﬁle to use (see Chapter 3 [Invoking Screen], page 5. Commands

in these ﬁles are used to set options, bind commands to keys, and to automatically establish

one or more windows at the beginning of your screen session. Commands are listed one

per line, with empty lines being ignored. A command’s arguments are separated by tabs

or spaces, and may be surrounded by single or double quotes. A ‘#’ turns the rest of the

line into a comment, except in quotes. Unintelligible lines are warned about and ignored.

Commands may contain references to environment variables. The syntax is the shell-like

$VAR or ${VAR}. Note that this causes incompatibility with previous screen versions, as

now the ’$’-character has to be protected with ’\’ if no variable substitution is intended. A

string in single-quotes is also protected from variable substitution.

Two conﬁguration ﬁles are shipped as examples with your screen distribution:

etc/screenrc and etc/etcscreenrc. They contain a number of useful examples for

various commands.

4.2 Source

[Command]source ﬁle

(none)

Read and execute commands from ﬁle ﬁle. Source commands may be nested to a

maximum recursion level of ten. If ﬁle is not an absolute path and screen is already

processing a source command, the parent directory of the running source command

ﬁle is used to search for the new command ﬁle before screen’s current directory.

Note that termcap/terminfo/termcapinfo commands only work at startup and reat-

tach time, so they must be reached via the default screenrc ﬁles to have an eﬀect.

4.3 Colon

Customization can also be done online, with this command:

[Command]colon

(C-a :)

Allows you to enter .screenrc command lines. Useful for on-the-ﬂy modiﬁcation

of key bindings, speciﬁc window creation and changing settings. Note that the set

keyword no longer exists, as of version 3.3. Change default settings with commands

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