背景
最近收拾东西，从一堆杂物里翻出来尘封四年多的树莓派 3B 主机来，打扫打扫灰尘，接上电源，居然还能通过之前设置好的 VNC 连上。欣慰之余，开始 clone 我的 git 项目，为它们拓展一个新的平台。在执行 cnblogs 项目 (参考《博客园排名预测 》) 对应的绘图命令时，趋势图、预测图是生成了，但没有自动打开图片，这个问题经过一番探索居然解决了，这篇文章就来分享一下解决问题的过程。
问题
第一眼看到的错误信息：
代码语言：javascript复制$ open ./fit.png
无法获取指向控制台的文件描述符这里我设置了控制台 locale 为中文，如果是英文的话，得到下面的结果：
代码语言：javascript复制Couldn't get a file descriptor referring to the console果断在网上搜索了这个错误，得到的结果比较少，根据解决方案主要分以下几种：
- setfont 命令：
- fedora - 错误：无法获得指向控制台的文件描述符
- Error in linux console : Couldn't get a file descriptor referring to the console
- loadkeys 命令：
- loadkeys says “Couldn't get a file descriptor referring to the console” in chroot on ChromeOS
这里我并没有调用 setfont 或 loadkeys 命令，直接执行它俩也会报一样的错误，难道需要在登录脚本里执行一下？抱着试试看的态度，我在 ~/.bashrc 中加了这么一句：
代码语言：javascript复制loadkeys重启树莓派，这回用 ssh 登录，结果一上来就报错：
代码语言：javascript复制The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Aug 8 23:07:46 2021 from 192.168.1.118
无法获取指向控制台的文件描述符看来网上的说法和我遇到的不一样，只能自己探索了。好在遇事不决、量子力学，哦 no，strace，看看底层调用哪个环节出问题了：
代码语言：javascript复制$ strace open ./fit.png
execve("/bin/open", ["open", "fit.png"], [/* 36 vars */]) = 0
brk(0) = 0x822000
uname({sys="Linux", node="raspberrypi", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f91000
access("/etc/ld.so.preload", R_OK) = 0
open("/etc/ld.so.preload", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=42, ...}) = 0
mmap2(NULL, 42, PROT_READ|PROT_WRITE, MAP_PRIVATE, 3, 0) = 0x76f90000
close(3) = 0
open("/usr/lib/arm-linux-gnueabihf/libarmmem.so", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 h5 004 "..., 512) = 512
lseek(3, 17960, SEEK_SET) = 17960
read(3, " "..., 960) = 960
lseek(3, 17696, SEEK_SET) = 17696
read(3, "A. aeabi 1$ 056 66101t1n3f122424"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0644, st_size=18920, ...}) = 0
mmap2(NULL, 83236, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76f4f000
mprotect(0x76f54000, 61440, PROT_NONE) = 0
mmap2(0x76f63000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x76f63000
mprotect(0x7eb5f000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC|PROT_GROWSDOWN) = 0
close(3) = 0
munmap(0x76f90000, 42) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=76981, ...}) = 0
mmap2(NULL, 76981, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76f3c000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 L2041 004 "..., 512) = 512
lseek(3, 1239936, SEEK_SET) = 1239936
read(3, " "..., 2840) = 2840
lseek(3, 1236500, SEEK_SET) = 1236500
read(3, "A. aeabi 1$ 056 66101t1n222423124"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0755, st_size=1242776, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f90000
mmap2(NULL, 1312152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76dfb000
mprotect(0x76f26000, 65536, PROT_NONE) = 0
mmap2(0x76f36000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12b000) = 0x76f36000
mmap2(0x76f39000, 9624, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x76f39000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f8f000
set_tls(0x76f8f4c0, 0x76f8fba8, 0x76f94050, 0x76f8f4c0, 0x76f94050) = 0
mprotect(0x76f36000, 8192, PROT_READ) = 0
mprotect(0x76f4f000, 20480, PROT_READ|PROT_WRITE) = 0
mprotect(0x76f4f000, 20480, PROT_READ|PROT_EXEC) = 0
cacheflush(0x76f4f000, 0x76f54000, 0, 0x15, 0x7eb5f0b0) = 0
mprotect(0x22000, 4096, PROT_READ) = 0
mprotect(0x76f93000, 4096, PROT_READ) = 0
munmap(0x76f3c000, 76981) = 0
brk(0) = 0x822000
brk(0x843000) = 0x843000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=4395328, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76bfb000
mmap2(NULL, 1720320, PROT_READ, MAP_PRIVATE, 3, 0x28e000) = 0x76a57000
close(3) = 0
fstat64(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
fstat64(1, {st_mode=S_IFREG|0644, st_size=3753, ...}) = 0
fstat64(2, {st_mode=S_IFREG|0644, st_size=3811, ...}) = 0
open("/proc/self/fd/0", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7eb5f14b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7eb5f14b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty0", O_RDWR) = -1 EACCES (Permission denied)
open("/dev/tty0", O_WRONLY) = -1 EACCES (Permission denied)
open("/dev/tty0", O_RDONLY) = -1 EACCES (Permission denied)
open("/dev/vc/0", O_RDWR) = -1 ENOENT (No such file or directory)
open("/dev/vc/0", O_WRONLY) = -1 ENOENT (No such file or directory)
open("/dev/vc/0", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/dev/systty", O_RDWR) = -1 ENOENT (No such file or directory)
open("/dev/systty", O_WRONLY) = -1 ENOENT (No such file or directory)
open("/dev/systty", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/dev/console", O_RDWR) = -1 EACCES (Permission denied)
open("/dev/console", O_WRONLY) = -1 EACCES (Permission denied)
open("/dev/console", O_RDONLY) = -1 EACCES (Permission denied)
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(0, KDGKBTYPE, 0x7eb5f14b) = -1 ENOTTY (Inappropriate ioctl for device)
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7eb5f0cc) = -1 ENOTTY (Inappropriate ioctl for device)
ioctl(2, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 0x7eb5f0cc) = -1 ENOTTY (Inappropriate ioctl for device)
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fcntl64(3, F_GETFD) = 0x1 (flags FD_CLOEXEC)
fstat64(3, {st_mode=S_IFREG|0644, st_size=2492, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f8e000
read(3, "# Locale name alias data base.n#"..., 4096) = 2492
read(3, "", 4096) = 0
close(3) = 0
munmap(0x76f8e000, 4096) = 0
open("/usr/share/locale/zh_CN.UTF-8/LC_MESSAGES/kbd.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/zh_CN.utf8/LC_MESSAGES/kbd.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/zh_CN/LC_MESSAGES/kbd.mo", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=30170, ...}) = 0
mmap2(NULL, 30170, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76f87000
close(3) = 0
open("/usr/lib/arm-linux-gnueabihf/gconv/gconv-modules.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=26262, ...}) = 0
mmap2(NULL, 26262, PROT_READ, MAP_SHARED, 3, 0) = 0x76f48000
close(3) = 0
write(2, "346227240346263225350216267345217226346214207345220221346216247345210266345217260347232204346226"..., 46无法获取指向控制台的文件描述符
) = 46
exit_group(1) = ?
exited with 1 brk (line 53) 之前的输出都不用看，属于程序初始化的逻辑；值得注意的报错点在 line 70 与 79：
代码语言：javascript复制open("/dev/console", O_RDWR) = -1 EACCES (Permission denied)这两个地方错误相似，都是打开 tty 设备时没有权限，而且是试了三种权限都失败了，分别为：读写 (O_RDWR)、只写 (O_WRONLY)、只读 (O_RDONLY)，看来为了打开这个设备，open 也是尽力了呀～
为什么好端端的会没有权限呢？让我们看下 ls 的输出：
代码语言：javascript复制$ ls -lh /dev/console
crw------- 1 root root 5, 1 Aug 8 22:37 /dev/console这个设备是 root 创建、root 拥有、且没有给其它用户开放任何权限，难怪会加载失败。
解决方案
既然根因是权限导致的，那就从权限入手来解决，之前系统总结过 linux 文件权限的规则 (参考 《[apue] linux 文件访问权限那些事儿 》)，要将 root 创建的文件分享给当前用户访问，也不是什么难事。
console group
第一个冒出来的想法，就是创建一个新的用户组 (例如 console)，把 root 和当前用户 pi 都加入到这个组中，然后指定设备的所有组为 console，并开放适当的组权限，这样就可以实现共享啦。有的人可能觉得麻烦，直接把出错的 tty 设备 chown 到当前用户不就行了？对于普通的数据文件，我也经常这样搞，但是对于公共的、系统相关的文件，我劝大家还是不要这么自信，否则可能搞到开不了机 (个人惨痛遭遇就不展开了)。另外这样做还有个额外的好处，就是当新用户遇到了同样问题时，只要把他加入这个组 (console) 就搞定了！下面是对应的脚本：
代码语言：javascript复制groups
sudo groupadd console
usermod -a -G console pi
groups
su
groups
usermod -a -G console root
groups
chgrp console /dev/console
chmod g rw /dev/console
exit夹在 usermod 前后的 groups 命令用来显示当前用户所属的用户组，用以验证添加附加组是否成功 (实际上无效，见后面说明)。注意对 root 帐户的操作需要使用 su 切换，切换后顺便对它拥有的文件 (/dev/console) 进行操作，以避免权限上的错误，最后执行完成后 exit 退回到当前用户。这里有两个点需要注意：
- usermod -a 选项必需和 -G 配合使用，之前我单独使用 -a 时 usemod 会直接打印 Usage，查了下 man 才弄明白；
- 将用户添加到一个组后 groups 不能立即看到结果，必需重新登录才会生效。特别对于 VNC 登录，logout 菜单似乎不起作用，需要重启设备才行。
觉得敲命令麻烦的同学，也可以直接进入 /etc/group 文件进行修改：
代码语言：javascript复制$ tail /etc/group
avahi:x:110:
ntp:x:111:
ssh:x:112:
bluetooth:x:113:
spi:x:999:pi
i2c:x:998:pi
gpio:x:997:pi
lightdm:x:114:
lpadmin:x:115:
console:x:1001:pi,root最后一行就是了。下面是执行成功后新的 ls 的输出：
代码语言：javascript复制# ls -lh /dev/console
crw-rw---- 1 root console 5, 1 Aug 8 22:37 /dev/console此时再运行一次 strace open，发现针对 console 的访问成功了！
代码语言：javascript复制open("/dev/console", O_RDWR) = 3虽然因为其它 tty 没有修改仍然出错了，但是至少证明方向是对的。
tty group
上面的方案是可行的，在查看 tty 设备时无意间得到了下面的输出：
代码语言：javascript复制$ ls -lh /dev/tty[0-9]*
crw------- 1 root root 4, 0 Aug 8 23:51 /dev/tty0
crw------- 1 pi tty 4, 1 Aug 8 23:52 /dev/tty1
crw------- 1 root tty 4, 10 Aug 8 23:51 /dev/tty10
crw------- 1 root tty 4, 11 Aug 8 23:51 /dev/tty11
crw------- 1 root tty 4, 12 Aug 8 23:51 /dev/tty12
crw------- 1 root tty 4, 13 Aug 8 23:51 /dev/tty13
crw------- 1 root tty 4, 14 Aug 8 23:51 /dev/tty14
crw------- 1 root tty 4, 15 Aug 8 23:51 /dev/tty15
crw------- 1 root tty 4, 16 Aug 8 23:51 /dev/tty16
crw------- 1 root tty 4, 17 Aug 8 23:51 /dev/tty17
crw------- 1 root tty 4, 18 Aug 8 23:51 /dev/tty18
crw------- 1 root tty 4, 19 Aug 8 23:51 /dev/tty19
crw------- 1 root root 4, 2 Aug 8 23:51 /dev/tty2
crw------- 1 root tty 4, 20 Aug 8 23:51 /dev/tty20
crw------- 1 root tty 4, 21 Aug 8 23:51 /dev/tty21
crw------- 1 root tty 4, 22 Aug 8 23:51 /dev/tty22
crw------- 1 root tty 4, 23 Aug 8 23:51 /dev/tty23
crw------- 1 root tty 4, 24 Aug 8 23:51 /dev/tty24
crw------- 1 root tty 4, 25 Aug 8 23:51 /dev/tty25
crw------- 1 root tty 4, 26 Aug 8 23:51 /dev/tty26
crw------- 1 root tty 4, 27 Aug 8 23:51 /dev/tty27
crw------- 1 root tty 4, 28 Aug 8 23:51 /dev/tty28
crw------- 1 root tty 4, 29 Aug 8 23:51 /dev/tty29
crw------- 1 root root 4, 3 Aug 8 23:51 /dev/tty3
crw------- 1 root tty 4, 30 Aug 8 23:51 /dev/tty30
crw------- 1 root tty 4, 31 Aug 8 23:51 /dev/tty31
crw------- 1 root tty 4, 32 Aug 8 23:51 /dev/tty32
crw------- 1 root tty 4, 33 Aug 8 23:51 /dev/tty33
crw------- 1 root tty 4, 34 Aug 8 23:51 /dev/tty34
crw------- 1 root tty 4, 35 Aug 8 23:51 /dev/tty35
crw------- 1 root tty 4, 36 Aug 8 23:51 /dev/tty36
crw------- 1 root tty 4, 37 Aug 8 23:51 /dev/tty37
crw------- 1 root tty 4, 38 Aug 8 23:51 /dev/tty38
crw------- 1 root tty 4, 39 Aug 8 23:51 /dev/tty39
crw------- 1 root tty 4, 4 Aug 8 23:51 /dev/tty4
crw------- 1 root tty 4, 40 Aug 8 23:51 /dev/tty40
crw------- 1 root tty 4, 41 Aug 8 23:51 /dev/tty41
crw------- 1 root tty 4, 42 Aug 8 23:51 /dev/tty42
crw------- 1 root tty 4, 43 Aug 8 23:51 /dev/tty43
crw------- 1 root tty 4, 44 Aug 8 23:51 /dev/tty44
crw------- 1 root tty 4, 45 Aug 8 23:51 /dev/tty45
crw------- 1 root tty 4, 46 Aug 8 23:51 /dev/tty46
crw------- 1 root tty 4, 47 Aug 8 23:51 /dev/tty47
crw------- 1 root tty 4, 48 Aug 8 23:51 /dev/tty48
crw------- 1 root tty 4, 49 Aug 8 23:51 /dev/tty49
crw------- 1 root tty 4, 5 Aug 8 23:51 /dev/tty5
crw------- 1 root tty 4, 50 Aug 8 23:51 /dev/tty50
crw------- 1 root tty 4, 51 Aug 8 23:51 /dev/tty51
crw------- 1 root tty 4, 52 Aug 8 23:51 /dev/tty52
crw------- 1 root tty 4, 53 Aug 8 23:51 /dev/tty53
crw------- 1 root tty 4, 54 Aug 8 23:51 /dev/tty54
crw------- 1 root tty 4, 55 Aug 8 23:51 /dev/tty55
crw------- 1 root tty 4, 56 Aug 8 23:51 /dev/tty56
crw------- 1 root tty 4, 57 Aug 8 23:51 /dev/tty57
crw------- 1 root tty 4, 58 Aug 8 23:51 /dev/tty58
crw------- 1 root tty 4, 59 Aug 8 23:51 /dev/tty59
crw------- 1 root tty 4, 6 Aug 8 23:51 /dev/tty6
crw------- 1 root tty 4, 60 Aug 8 23:51 /dev/tty60
crw------- 1 root tty 4, 61 Aug 8 23:51 /dev/tty61
crw------- 1 root tty 4, 62 Aug 8 23:51 /dev/tty62
crw------- 1 root tty 4, 63 Aug 8 23:51 /dev/tty63
crw------- 1 root tty 4, 7 Aug 8 23:51 /dev/tty7
crw------- 1 root tty 4, 8 Aug 8 23:51 /dev/tty8
crw------- 1 root tty 4, 9 Aug 8 23:51 /dev/tty9除了 tty0 / tty2 / tty3 的用户组属于 root 外，其它 tty 设备都属于 tty 用户组，原来系统早为它们准备了现成的组，我在上面创建 console 组就显得画蛇添足了，而且观察用户 pi 所属的附加组：
代码语言：javascript复制$ groups
pi adm tty dialout cdrom sudo audio video plugdev games users input netdev gpio i2c spi console其中一个就是 tty，所以我从善如流的决定使用使用 tty 了。因此上节的脚本可以简化为：
代码语言：javascript复制su
chgrp tty /dev/console /dev/tty[0-9]*
chmod g rw /dev/console /dev/tty[0-9]*
exit什么创建用户组、为用户添加附加组统统可以不要了，只需要修正 tty 设备文件的用户组就可以啦。
group permission
重启设备让修改生效后，再运行一次 strace open，发现还是有问题：
代码语言：javascript复制$ strace open ./fit.png
execve("/bin/open", ["open", "./fit.png"], [/* 36 vars */]) = 0
brk(0) = 0xe6b000
uname({sys="Linux", node="raspberrypi", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f95000
access("/etc/ld.so.preload", R_OK) = 0
open("/etc/ld.so.preload", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=42, ...}) = 0
mmap2(NULL, 42, PROT_READ|PROT_WRITE, MAP_PRIVATE, 3, 0) = 0x76f94000
close(3) = 0
open("/usr/lib/arm-linux-gnueabihf/libarmmem.so", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 h5 004 "..., 512) = 512
lseek(3, 17960, SEEK_SET) = 17960
read(3, " "..., 960) = 960
lseek(3, 17696, SEEK_SET) = 17696
read(3, "A. aeabi 1$ 056 66101t1n3f122424"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0644, st_size=18920, ...}) = 0
mmap2(NULL, 83236, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76f53000
mprotect(0x76f58000, 61440, PROT_NONE) = 0
mmap2(0x76f67000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x76f67000
mprotect(0x7e817000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC|PROT_GROWSDOWN) = 0
close(3) = 0
munmap(0x76f94000, 42) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=76981, ...}) = 0
mmap2(NULL, 76981, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76f40000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 L2041 004 "..., 512) = 512
lseek(3, 1239936, SEEK_SET) = 1239936
read(3, " "..., 2840) = 2840
lseek(3, 1236500, SEEK_SET) = 1236500
read(3, "A. aeabi 1$ 056 66101t1n222423124"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0755, st_size=1242776, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f94000
mmap2(NULL, 1312152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76dff000
mprotect(0x76f2a000, 65536, PROT_NONE) = 0
mmap2(0x76f3a000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12b000) = 0x76f3a000
mmap2(0x76f3d000, 9624, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x76f3d000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76f93000
set_tls(0x76f934c0, 0x76f93ba8, 0x76f98050, 0x76f934c0, 0x76f98050) = 0
mprotect(0x76f3a000, 8192, PROT_READ) = 0
mprotect(0x76f53000, 20480, PROT_READ|PROT_WRITE) = 0
mprotect(0x76f53000, 20480, PROT_READ|PROT_EXEC) = 0
cacheflush(0x76f53000, 0x76f58000, 0, 0x15, 0x7e8170b0) = 0
mprotect(0x22000, 4096, PROT_READ) = 0
mprotect(0x76f97000, 4096, PROT_READ) = 0
munmap(0x76f40000, 76981) = 0
brk(0) = 0xe6b000
brk(0xe8c000) = 0xe8c000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=4395328, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76bff000
mmap2(NULL, 1720320, PROT_READ, MAP_PRIVATE, 3, 0x28e000) = 0x76a5b000
close(3) = 0
fstat64(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
fstat64(1, {st_mode=S_IFREG|0644, st_size=3755, ...}) = 0
fstat64(2, {st_mode=S_IFREG|0644, st_size=3813, ...}) = 0
open("/proc/self/fd/0", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7e81714b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7e81714b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty0", O_RDWR) = -1 EACCES (Permission denied)
open("/dev/tty0", O_WRONLY) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 -opost -isig -icanon -echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7e81714b) = 0
ioctl(3, VT_GETSTATE, 0x7e8171a8) = 0
ioctl(3, VIDIOC_QUERYCAP or VT_OPENQRY, 0x7e8171a4) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x76f93068) = 1882
exit_group(0) = ?
exited with 0
open: Unable to open /dev/tty2: 权限不够line 70 有一次失败，但是马上 line 71 对同一个设备操作成功，末尾出现的权限不够失败对应的 /dev/tty2 文件根本在前面没有出现过，amazing～
用 ls 大法看一看：
代码语言：javascript复制$ ls -lh /dev/tty[0-9]*
crw--w---- 1 root tty 4, 0 Aug 9 00:13 /dev/tty0
crw------- 1 pi tty 4, 1 Aug 9 00:14 /dev/tty1
crw--w---- 1 root tty 4, 10 Aug 9 00:13 /dev/tty10
crw--w---- 1 root tty 4, 11 Aug 9 00:13 /dev/tty11
crw--w---- 1 root tty 4, 12 Aug 9 00:13 /dev/tty12
crw--w---- 1 root tty 4, 13 Aug 9 00:13 /dev/tty13
crw--w---- 1 root tty 4, 14 Aug 9 00:13 /dev/tty14
crw--w---- 1 root tty 4, 15 Aug 9 00:13 /dev/tty15
crw--w---- 1 root tty 4, 16 Aug 9 00:13 /dev/tty16
crw--w---- 1 root tty 4, 17 Aug 9 00:13 /dev/tty17
crw--w---- 1 root tty 4, 18 Aug 9 00:13 /dev/tty18
crw--w---- 1 root tty 4, 19 Aug 9 00:13 /dev/tty19
crw--w---- 1 root tty 4, 2 Aug 9 00:13 /dev/tty2
crw--w---- 1 root tty 4, 20 Aug 9 00:13 /dev/tty20
crw--w---- 1 root tty 4, 21 Aug 9 00:13 /dev/tty21
crw--w---- 1 root tty 4, 22 Aug 9 00:13 /dev/tty22
crw--w---- 1 root tty 4, 23 Aug 9 00:13 /dev/tty23
crw--w---- 1 root tty 4, 24 Aug 9 00:13 /dev/tty24
crw--w---- 1 root tty 4, 25 Aug 9 00:13 /dev/tty25
crw--w---- 1 root tty 4, 26 Aug 9 00:13 /dev/tty26
crw--w---- 1 root tty 4, 27 Aug 9 00:13 /dev/tty27
crw--w---- 1 root tty 4, 28 Aug 9 00:13 /dev/tty28
crw--w---- 1 root tty 4, 29 Aug 9 00:13 /dev/tty29
crw--w---- 1 root tty 4, 3 Aug 9 00:13 /dev/tty3
crw--w---- 1 root tty 4, 30 Aug 9 00:13 /dev/tty30
crw--w---- 1 root tty 4, 31 Aug 9 00:13 /dev/tty31
crw--w---- 1 root tty 4, 32 Aug 9 00:13 /dev/tty32
crw--w---- 1 root tty 4, 33 Aug 9 00:13 /dev/tty33
crw--w---- 1 root tty 4, 34 Aug 9 00:13 /dev/tty34
crw--w---- 1 root tty 4, 35 Aug 9 00:13 /dev/tty35
crw--w---- 1 root tty 4, 36 Aug 9 00:13 /dev/tty36
crw--w---- 1 root tty 4, 37 Aug 9 00:13 /dev/tty37
crw--w---- 1 root tty 4, 38 Aug 9 00:13 /dev/tty38
crw--w---- 1 root tty 4, 39 Aug 9 00:13 /dev/tty39
crw--w---- 1 root tty 4, 4 Aug 9 00:13 /dev/tty4
crw--w---- 1 root tty 4, 40 Aug 9 00:13 /dev/tty40
crw--w---- 1 root tty 4, 41 Aug 9 00:13 /dev/tty41
crw--w---- 1 root tty 4, 42 Aug 9 00:13 /dev/tty42
crw--w---- 1 root tty 4, 43 Aug 9 00:13 /dev/tty43
crw--w---- 1 root tty 4, 44 Aug 9 00:13 /dev/tty44
crw--w---- 1 root tty 4, 45 Aug 9 00:13 /dev/tty45
crw--w---- 1 root tty 4, 46 Aug 9 00:13 /dev/tty46
crw--w---- 1 root tty 4, 47 Aug 9 00:13 /dev/tty47
crw--w---- 1 root tty 4, 48 Aug 9 00:13 /dev/tty48
crw--w---- 1 root tty 4, 49 Aug 9 00:13 /dev/tty49
crw--w---- 1 root tty 4, 5 Aug 9 00:13 /dev/tty5
crw--w---- 1 root tty 4, 50 Aug 9 00:13 /dev/tty50
crw--w---- 1 root tty 4, 51 Aug 9 00:13 /dev/tty51
crw--w---- 1 root tty 4, 52 Aug 9 00:13 /dev/tty52
crw--w---- 1 root tty 4, 53 Aug 9 00:13 /dev/tty53
crw--w---- 1 root tty 4, 54 Aug 9 00:13 /dev/tty54
crw--w---- 1 root tty 4, 55 Aug 9 00:13 /dev/tty55
crw--w---- 1 root tty 4, 56 Aug 9 00:13 /dev/tty56
crw--w---- 1 root tty 4, 57 Aug 9 00:13 /dev/tty57
crw--w---- 1 root tty 4, 58 Aug 9 00:13 /dev/tty58
crw--w---- 1 root tty 4, 59 Aug 9 00:13 /dev/tty59
crw--w---- 1 root tty 4, 6 Aug 9 00:13 /dev/tty6
crw--w---- 1 root tty 4, 60 Aug 9 00:13 /dev/tty60
crw--w---- 1 root tty 4, 61 Aug 9 00:13 /dev/tty61
crw--w---- 1 root tty 4, 62 Aug 9 00:13 /dev/tty62
crw--w---- 1 root tty 4, 63 Aug 9 00:13 /dev/tty63
crw--w---- 1 root tty 4, 7 Aug 9 00:13 /dev/tty7
crw--w---- 1 root tty 4, 8 Aug 9 00:13 /dev/tty8
crw--w---- 1 root tty 4, 9 Aug 9 00:13 /dev/tty9所有 tty 设置的组权限变成了只写？难道是上一步中重启设备前我忘了设置各个文件的权限? 用 root 帐号 chmod 一下，输出这次正常了：
代码语言：javascript复制$ strace open ./fit.png
execve("/bin/open", ["open", "./fit.png"], [/* 36 vars */]) = 0
brk(0) = 0x288000
uname({sys="Linux", node="raspberrypi", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76efd000
access("/etc/ld.so.preload", R_OK) = 0
open("/etc/ld.so.preload", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=42, ...}) = 0
mmap2(NULL, 42, PROT_READ|PROT_WRITE, MAP_PRIVATE, 3, 0) = 0x76efc000
close(3) = 0
open("/usr/lib/arm-linux-gnueabihf/libarmmem.so", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 h5 004 "..., 512) = 512
lseek(3, 17960, SEEK_SET) = 17960
read(3, " "..., 960) = 960
lseek(3, 17696, SEEK_SET) = 17696
read(3, "A. aeabi 1$ 056 66101t1n3f122424"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0644, st_size=18920, ...}) = 0
mmap2(NULL, 83236, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76ebb000
mprotect(0x76ec0000, 61440, PROT_NONE) = 0
mmap2(0x76ecf000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x76ecf000
mprotect(0x7ea80000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC|PROT_GROWSDOWN) = 0
close(3) = 0
munmap(0x76efc000, 42) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=76981, ...}) = 0
mmap2(NULL, 76981, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76ea8000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/arm-linux-gnueabihf/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF111 3 ( 1 L2041 004 "..., 512) = 512
lseek(3, 1239936, SEEK_SET) = 1239936
read(3, " "..., 2840) = 2840
lseek(3, 1236500, SEEK_SET) = 1236500
read(3, "A. aeabi 1$ 056 66101t1n222423124"..., 47) = 47
fstat64(3, {st_mode=S_IFREG|0755, st_size=1242776, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76efc000
mmap2(NULL, 1312152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x76d67000
mprotect(0x76e92000, 65536, PROT_NONE) = 0
mmap2(0x76ea2000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12b000) = 0x76ea2000
mmap2(0x76ea5000, 9624, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x76ea5000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x76efb000
set_tls(0x76efb4c0, 0x76efbba8, 0x76f00050, 0x76efb4c0, 0x76f00050) = 0
mprotect(0x76ea2000, 8192, PROT_READ) = 0
mprotect(0x76ebb000, 20480, PROT_READ|PROT_WRITE) = 0
mprotect(0x76ebb000, 20480, PROT_READ|PROT_EXEC) = 0
cacheflush(0x76ebb000, 0x76ec0000, 0, 0x15, 0x7ea800b0) = 0
mprotect(0x22000, 4096, PROT_READ) = 0
mprotect(0x76eff000, 4096, PROT_READ) = 0
munmap(0x76ea8000, 76981) = 0
brk(0) = 0x288000
brk(0x2a9000) = 0x2a9000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=4395328, ...}) = 0
mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x76b67000
mmap2(NULL, 1720320, PROT_READ, MAP_PRIVATE, 3, 0x28e000) = 0x769c3000
close(3) = 0
fstat64(0, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
fstat64(1, {st_mode=S_IFREG|0644, st_size=3755, ...}) = 0
fstat64(2, {st_mode=S_IFREG|0644, st_size=3813, ...}) = 0
open("/proc/self/fd/0", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ea8014b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ea8014b) = -1 ENOTTY (Inappropriate ioctl for device)
close(3) = 0
open("/dev/tty0", O_RDWR) = 3
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 -opost -isig -icanon -echo ...}) = 0
ioctl(3, KDGKBTYPE, 0x7ea8014b) = 0
ioctl(3, VT_GETSTATE, 0x7ea801a8) = 0
ioctl(3, VIDIOC_QUERYCAP or VT_OPENQRY, 0x7ea801a4) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x76efb068) = 2013
exit_group(0) = ?
exited with 0 不过再次重启后，这个文件权限仍然会被重置，之前使用 console group 时，也发现重启设备后 /dev/console 文件的用户组会自动重置为 root，组权限重置为空。好在这里只是将权限重置为只写，难道每次登录都要设置一遍 tty 文件权限？
xdg-open
答案是 no，倒不是因为找到了解决方案，而是即使在权限正确的情况下、open 不再报错了，图片还是没有自动打开 (汗)。于是我决定试试其它的命令，经过一番百度，找到了一个在 Ubuntu 下很常用的 xdg-open 命令，参数是要打开的图片路径，调用方式和 open 一样。话说回来，open 是我在 mac 上使用的命令，不适用 raspberrypi 是情理之中的，至于这个上的 open 是干啥的，我没找到对应的 man 记录 (还是个三无命令)。另外一开始如果使用 xdg-open，是不是就不用设置设备文件的用户组和权限了？没有试，不得而知。
结语
本文探索了诡异的 tty 设备文件权限问题，结合 linux 文件权限相关的知识进行了一番大胆的尝试，最后却另辟蹊径解决了问题。如果你在现实中遇到了类似的问题，不妨可以试试上面的方案，不管成功与否，都欢迎在文章下面留言反馈。
后记
和问题相关的都说的差不多了，下面来聊两句题外话。这次收拾尘封的树莓派，我深切的体会到了设置密码要简单的重要性，ssh 登录过程中试遍了我常用的所有密码，都不行，最后还是 1-6 拯救了我，而且 root 密码也是这个呦～
最后看着破破烂烂的亚克力塑料外壳，实在不能忍了，果断淘宝了一套新的外壳换上，换壳前后对比明显：
最后上一张树莓派 VNC 的截图：
参考
1. Ubuntu下通过命令打开图片
