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David Purdy's questions

Martin Hope
David Purdy
Asked: 2023-02-17 20:44:35 +0800 CST
  • 6

为什么不能ls使用我的脚本 cron /dev 中的某些文件？

从命令行运行时，该脚本可以完整列出 /dev。从任一 cron 设置运行的相同脚本无法看到 (list, ls) /dev 中的大部分文件。无论哪种方式，脚本都以 root 身份运行，具有几乎相同的 env 值，结果却大不相同。/dev 中大约有 100 个文件无法访问，包括所有磁盘，因此mount无法从 cron 进行操作。（Debian 11.6 最小网络全新安装，没有 SELinux 或 Apparmor，没有容器。）

下面是一个揭示这种令人费解的行为的诊断脚本。脚本本身除了说明和阐明这些行为外没有任何用处，但是 cron 任务查看某些关键文件（例如，挂载文件系统、使用 df 检查空间等）的能力是至关重要的。

#!/bin/bash

#  turn on some tracing, get a timestamp, printenv, whoami
set -xa
echo "timestamp: $(date)"
echo "env values:"
printenv
whoami


cd /
echo "ls -la"
ls -la
cd /dev
echo "cd to /dev, then ls -la"
ls -la
cd disk
echo "cd to /dev/disk, then ls -la"
ls -la

echo " "
echo "just because someone might ask, try to ls /dev/disk directly from /"
cd /
ls -la /dev/disk

命令行输出：

++ date
+ echo 'timestamp: Thu 16 Feb 2023 10:05:33 PM CST'
timestamp: Thu 16 Feb 2023 10:05:33 PM CST
+ echo 'env values:'
env values:
+ printenv
SHELL=/bin/bash
PWD=/usr/local/bin
LOGNAME=root
TEMPDIR=/tmp/user/0
HOME=/root
LANG=en_US.UTF-8
TMPDIR=/tmp/user/0
TERM=xterm-256color
USER=root
TEMP=/tmp/user/0
SHLVL=2
TMP=/tmp/user/0
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
MAIL=/var/mail/root
OLDPWD=/
_=/usr/bin/printenv
+ whoami
root
+ cd /
+ echo 'ls -la'
ls -la
+ ls -la
total 68
drwxr-xr-x  18 root root  4096 Feb 16 21:19 .
drwxr-xr-x  18 root root  4096 Feb 16 21:19 ..
lrwxrwxrwx   1 root root     7 Feb  7 19:48 bin -> usr/bin
drwxr-xr-x   4 root root  4096 Feb 12 20:57 boot
drwxr-xr-x  17 root root  3300 Feb 16 16:53 dev
drwxr-xr-x  99 root root  4096 Feb 16 17:09 etc
drwxr-xr-x   4 root root  4096 Feb  9 18:58 home
lrwxrwxrwx   1 root root    31 Feb  7 19:51 initrd.img -> boot/initrd.img-5.10.0-21-amd64
lrwxrwxrwx   1 root root    31 Feb  7 19:49 initrd.img.old -> boot/initrd.img-5.10.0-20-amd64
lrwxrwxrwx   1 root root     7 Feb  7 19:48 lib -> usr/lib
lrwxrwxrwx   1 root root     9 Feb  7 19:48 lib32 -> usr/lib32
lrwxrwxrwx   1 root root     9 Feb  7 19:48 lib64 -> usr/lib64
lrwxrwxrwx   1 root root    10 Feb  7 19:48 libx32 -> usr/libx32
drwx------   2 root root 16384 Feb  7 19:48 lost+found
drwxr-xr-x   3 root root  4096 Feb  7 19:49 media
drwxr-xr-x   7 root root  4096 Feb 16 20:42 mnt
drwxr-xr-x   2 root root  4096 Feb  7 19:48 opt
dr-xr-xr-x 182 root root     0 Feb 16 16:53 proc
drwx------   5 root root  4096 Feb 16 21:05 root
drwxr-xr-x  24 root root   780 Feb 16 16:58 run
lrwxrwxrwx   1 root root     8 Feb  7 19:48 sbin -> usr/sbin
drwxr-xr-x   2 root root  4096 Feb  7 19:48 srv
dr-xr-xr-x  13 root root     0 Feb 16 16:53 sys
drwxrwxrwt  11 root root  4096 Feb 16 22:04 tmp
drwxr-xr-x  14 root root  4096 Feb  7 19:48 usr
drwxr-xr-x  12 root root  4096 Feb  7 20:14 var
lrwxrwxrwx   1 root root    28 Feb  7 19:51 vmlinuz -> boot/vmlinuz-5.10.0-21-amd64
lrwxrwxrwx   1 root root    28 Feb  7 19:49 vmlinuz.old -> boot/vmlinuz-5.10.0-20-amd64
+ cd /dev
+ echo 'cd to /dev, then ls -la'
cd to /dev, then ls -la
+ ls -la
total 4
drwxr-xr-x 17 root root        3.3K Feb 16 16:53 .
drwxr-xr-x 18 root root        4.0K Feb 16 21:19 ..
crw-r--r--  1 root root     10, 235 Feb 16 16:53 autofs
drwxr-xr-x  2 root root         200 Feb 16 16:53 block
drwxr-xr-x  2 root root          80 Feb 16 16:53 bsg
crw-------  1 root root     10, 234 Feb 16 16:53 btrfs-control
drwxr-xr-x  3 root root          60 Feb 16 16:53 bus
drwxr-xr-x  2 root root        3.1K Feb 16 16:53 char
crw--w----  1 root tty       5,   1 Feb 16 16:53 console
lrwxrwxrwx  1 root root          11 Feb 16 16:53 core -> /proc/kcore
crw-------  1 root root     10,  62 Feb 16 16:53 cpu_dma_latency
crw-------  1 root root     10, 203 Feb 16 16:53 cuse
drwxr-xr-x  7 root root         140 Feb 16 16:53 disk
drwxr-xr-x  3 root root         100 Feb 16 16:53 dri
crw-------  1 root root    246,   0 Feb 16 16:53 drm_dp_aux0
lrwxrwxrwx  1 root root          13 Feb 16 16:53 fd -> /proc/self/fd
crw-rw-rw-  1 root root      1,   7 Feb 16 16:53 full
crw-rw-rw-  1 root root     10, 229 Feb 16 16:53 fuse
crw-------  1 root root     10, 228 Feb 16 16:53 hpet
drwxr-xr-x  2 root root           0 Feb 16 16:53 hugepages
crw-------  1 root root     10, 183 Feb 16 16:53 hwrng
lrwxrwxrwx  1 root root          12 Feb 16 16:53 initctl -> /run/initctl
drwxr-xr-x  3 root root         280 Feb 16 16:53 input
crw-r--r--  1 root root      1,  11 Feb 16 16:53 kmsg
crw-rw----  1 root kvm      10, 232 Feb 16 16:53 kvm
lrwxrwxrwx  1 root root          28 Feb 16 16:53 log -> /run/systemd/journal/dev-log
crw-rw----  1 root disk     10, 237 Feb 16 16:53 loop-control
drwxr-xr-x  2 root root          60 Feb 16 16:53 mapper
crw-------  1 root root    249,   0 Feb 16 16:53 mei0
crw-r-----  1 root kmem      1,   1 Feb 16 16:53 mem
drwxrwxrwt  2 root root          40 Feb 16 16:53 mqueue
drwxr-xr-x  2 root root          60 Feb 16 16:53 net
crw-rw-rw-  1 root root      1,   3 Feb 16 16:53 null
crw-------  1 root root     10, 144 Feb 16 16:53 nvram
crw-r-----  1 root kmem      1,   4 Feb 16 16:53 port
crw-------  1 root root    108,   0 Feb 16 16:53 ppp
crw-------  1 root root     10,   1 Feb 16 16:53 psaux
crw-rw-rw-  1 root tty       5,   2 Feb 16  2023 ptmx
drwxr-xr-x  2 root root           0 Feb 16 16:53 pts
crw-rw-rw-  1 root root      1,   8 Feb 16 16:53 random
crw-rw-r--  1 root netdev   10, 242 Feb 16 16:53 rfkill
lrwxrwxrwx  1 root root           4 Feb 16 16:53 rtc -> rtc0
crw-------  1 root root    252,   0 Feb 16 16:53 rtc0
brw-rw----  1 root disk      8,   0 Feb 16 16:53 sda
brw-rw----  1 root disk      8,   1 Feb 16 16:53 sda1
brw-rw----  1 root disk      8,   2 Feb 16 16:53 sda2
brw-rw----  1 root disk      8,   3 Feb 16 16:53 sda3
brw-rw----  1 root disk      8,  16 Feb 16 16:53 sdb
brw-rw----  1 root disk      8,  17 Feb 16 16:53 sdb1
brw-rw----  1 root disk      8,  18 Feb 16 16:53 sdb2
brw-rw----  1 root disk      8,  19 Feb 16 16:53 sdb3
crw-rw----  1 root disk     21,   0 Feb 16 16:53 sg0
crw-rw----  1 root disk     21,   1 Feb 16 16:53 sg1
drwxrwxrwt  2 root root          40 Feb 16 16:53 shm
crw-------  1 root root     10, 231 Feb 16 16:53 snapshot
drwxr-xr-x  3 root root         320 Feb 16 16:53 snd
lrwxrwxrwx  1 root root          15 Feb 16 16:53 stderr -> /proc/self/fd/2
lrwxrwxrwx  1 root root          15 Feb 16 16:53 stdin -> /proc/self/fd/0
lrwxrwxrwx  1 root root          15 Feb 16 16:53 stdout -> /proc/self/fd/1
crw-------  1 root root     10, 224 Feb 16 16:53 tpm0
crw-rw-rw-  1 root tty       5,   0 Feb 16 21:13 tty
crw--w----  1 root tty       4,   0 Feb 16 16:53 tty0
crw--w----  1 root tty       4,   1 Feb 16 16:53 tty1
crw--w----  1 root tty       4,  10 Feb 16 16:53 tty10
crw--w----  1 root tty       4,  11 Feb 16 16:53 tty11
crw--w----  1 root tty       4,  12 Feb 16 16:53 tty12
crw--w----  1 root tty       4,  13 Feb 16 16:53 tty13
crw--w----  1 root tty       4,  14 Feb 16 16:53 tty14
crw--w----  1 root tty       4,  15 Feb 16 16:53 tty15
crw--w----  1 root tty       4,  16 Feb 16 16:53 tty16
crw--w----  1 root tty       4,  17 Feb 16 16:53 tty17
crw--w----  1 root tty       4,  18 Feb 16 16:53 tty18
crw--w----  1 root tty       4,  19 Feb 16 16:53 tty19
crw--w----  1 root tty       4,   2 Feb 16 16:53 tty2
crw--w----  1 root tty       4,  20 Feb 16 16:53 tty20
crw--w----  1 root tty       4,  21 Feb 16 16:53 tty21
crw--w----  1 root tty       4,  22 Feb 16 16:53 tty22
crw--w----  1 root tty       4,  23 Feb 16 16:53 tty23
crw--w----  1 root tty       4,  24 Feb 16 16:53 tty24
crw--w----  1 root tty       4,  25 Feb 16 16:53 tty25
crw--w----  1 root tty       4,  26 Feb 16 16:53 tty26
crw--w----  1 root tty       4,  27 Feb 16 16:53 tty27
crw--w----  1 root tty       4,  28 Feb 16 16:53 tty28
crw--w----  1 root tty       4,  29 Feb 16 16:53 tty29
crw--w----  1 root tty       4,   3 Feb 16 16:53 tty3
crw--w----  1 root tty       4,  30 Feb 16 16:53 tty30
crw--w----  1 root tty       4,  31 Feb 16 16:53 tty31
crw--w----  1 root tty       4,  32 Feb 16 16:53 tty32
crw--w----  1 root tty       4,  33 Feb 16 16:53 tty33
crw--w----  1 root tty       4,  34 Feb 16 16:53 tty34
crw--w----  1 root tty       4,  35 Feb 16 16:53 tty35
crw--w----  1 root tty       4,  36 Feb 16 16:53 tty36
crw--w----  1 root tty       4,  37 Feb 16 16:53 tty37
crw--w----  1 root tty       4,  38 Feb 16 16:53 tty38
crw--w----  1 root tty       4,  39 Feb 16 16:53 tty39
crw--w----  1 root tty       4,   4 Feb 16 16:53 tty4
crw--w----  1 root tty       4,  40 Feb 16 16:53 tty40
crw--w----  1 root tty       4,  41 Feb 16 16:53 tty41
crw--w----  1 root tty       4,  42 Feb 16 16:53 tty42
crw--w----  1 root tty       4,  43 Feb 16 16:53 tty43
crw--w----  1 root tty       4,  44 Feb 16 16:53 tty44
crw--w----  1 root tty       4,  45 Feb 16 16:53 tty45
crw--w----  1 root tty       4,  46 Feb 16 16:53 tty46
crw--w----  1 root tty       4,  47 Feb 16 16:53 tty47
crw--w----  1 root tty       4,  48 Feb 16 16:53 tty48
crw--w----  1 root tty       4,  49 Feb 16 16:53 tty49
crw--w----  1 root tty       4,   5 Feb 16 16:53 tty5
crw--w----  1 root tty       4,  50 Feb 16 16:53 tty50
crw--w----  1 root tty       4,  51 Feb 16 16:53 tty51
crw--w----  1 root tty       4,  52 Feb 16 16:53 tty52
crw--w----  1 root tty       4,  53 Feb 16 16:53 tty53
crw--w----  1 root tty       4,  54 Feb 16 16:53 tty54
crw--w----  1 root tty       4,  55 Feb 16 16:53 tty55
crw--w----  1 root tty       4,  56 Feb 16 16:53 tty56
crw--w----  1 root tty       4,  57 Feb 16 16:53 tty57
crw--w----  1 root tty       4,  58 Feb 16 16:53 tty58
crw--w----  1 root tty       4,  59 Feb 16 16:53 tty59
crw--w----  1 root tty       4,   6 Feb 16 16:53 tty6
crw--w----  1 root tty       4,  60 Feb 16 16:53 tty60
crw--w----  1 root tty       4,  61 Feb 16 16:53 tty61
crw--w----  1 root tty       4,  62 Feb 16 16:53 tty62
crw--w----  1 root tty       4,  63 Feb 16 16:53 tty63
crw--w----  1 root tty       4,   7 Feb 16 16:53 tty7
crw--w----  1 root tty       4,   8 Feb 16 16:53 tty8
crw--w----  1 root tty       4,   9 Feb 16 16:53 tty9
crw-rw----  1 root dialout   4,  64 Feb 16 16:53 ttyS0
crw-rw----  1 root dialout   4,  65 Feb 16 16:53 ttyS1
crw-rw----  1 root dialout   4,  66 Feb 16 16:53 ttyS2
crw-rw----  1 root dialout   4,  67 Feb 16 16:53 ttyS3
crw-------  1 root root     10, 239 Feb 16 16:53 uhid
crw-------  1 root root     10, 223 Feb 16 16:53 uinput
crw-rw-rw-  1 root root      1,   9 Feb 16 16:53 urandom
crw-rw----  1 root tty       7,   0 Feb 16 16:53 vcs
crw-rw----  1 root tty       7,   1 Feb 16 16:53 vcs1
crw-rw----  1 root tty       7,  10 Feb 16 16:53 vcs10
crw-rw----  1 root tty       7,   2 Feb 16 16:53 vcs2
crw-rw----  1 root tty       7,   3 Feb 16 16:53 vcs3
crw-rw----  1 root tty       7,   4 Feb 16 16:53 vcs4
crw-rw----  1 root tty       7,   5 Feb 16 16:53 vcs5
crw-rw----  1 root tty       7,   6 Feb 16 16:53 vcs6
crw-rw----  1 root tty       7, 128 Feb 16 16:53 vcsa
crw-rw----  1 root tty       7, 129 Feb 16 16:53 vcsa1
crw-rw----  1 root tty       7, 138 Feb 16 16:53 vcsa10
crw-rw----  1 root tty       7, 130 Feb 16 16:53 vcsa2
crw-rw----  1 root tty       7, 131 Feb 16 16:53 vcsa3
crw-rw----  1 root tty       7, 132 Feb 16 16:53 vcsa4
crw-rw----  1 root tty       7, 133 Feb 16 16:53 vcsa5
crw-rw----  1 root tty       7, 134 Feb 16 16:53 vcsa6
crw-rw----  1 root tty       7,  64 Feb 16 16:53 vcsu
crw-rw----  1 root tty       7,  65 Feb 16 16:53 vcsu1
crw-rw----  1 root tty       7,  74 Feb 16 16:53 vcsu10
crw-rw----  1 root tty       7,  66 Feb 16 16:53 vcsu2
crw-rw----  1 root tty       7,  67 Feb 16 16:53 vcsu3
crw-rw----  1 root tty       7,  68 Feb 16 16:53 vcsu4
crw-rw----  1 root tty       7,  69 Feb 16 16:53 vcsu5
crw-rw----  1 root tty       7,  70 Feb 16 16:53 vcsu6
drwxr-xr-x  2 root root          60 Feb 16 16:53 vfio
crw-------  1 root root     10,  63 Feb 16 16:53 vga_arbiter
crw-------  1 root root     10, 137 Feb 16 16:53 vhci
crw-------  1 root root     10, 238 Feb 16 16:53 vhost-net
crw-------  1 root root     10, 241 Feb 16 16:53 vhost-vsock
crw-------  1 root root     10, 130 Feb 16 16:53 watchdog
crw-------  1 root root    247,   0 Feb 16 16:53 watchdog0
prw-r-----  1 root adm            0 Feb 16 16:53 xconsole
crw-rw-rw-  1 root root      1,   5 Feb 16 16:53 zero
+ cd disk
+ echo 'cd to /dev/disk, then ls -la'
cd to /dev/disk, then ls -la
+ ls -la
total 0
drwxr-xr-x  7 root root  140 Feb 16 16:53 .
drwxr-xr-x 17 root root 3300 Feb 16 16:53 ..
drwxr-xr-x  2 root root  280 Feb 16 16:53 by-id
drwxr-xr-x  2 root root  100 Feb 16 16:53 by-partlabel
drwxr-xr-x  2 root root  100 Feb 16 16:53 by-partuuid
drwxr-xr-x  2 root root  280 Feb 16 16:53 by-path
drwxr-xr-x  2 root root  140 Feb 16 16:53 by-uuid
+ echo ' '
 
+ echo 'just because someone might ask, try to ls /dev/disk directly from /'
just because someone might ask, try to ls /dev/disk directly from /
+ cd /
+ ls -la /dev/disk
total 0
drwxr-xr-x  7 root root  140 Feb 16 16:53 .
drwxr-xr-x 17 root root 3300 Feb 16 16:53 ..
drwxr-xr-x  2 root root  280 Feb 16 16:53 by-id
drwxr-xr-x  2 root root  100 Feb 16 16:53 by-partlabel
drwxr-xr-x  2 root root  100 Feb 16 16:53 by-partuuid
drwxr-xr-x  2 root root  280 Feb 16 16:53 by-path
drwxr-xr-x  2 root root  140 Feb 16 16:53 by-uuid

crontab 条目：（尝试不带 env 变量，然后逐渐添加它们）

SHELL=/bin/bash
BASH_ENV="/root/.bashrc"
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
USER=root
* * * * * /usr/local/bin/problem > /var/log/backup/problem.log 2>&1

crontab 的输出：（注意与大多数命令行输出的相似性，除了 /dev 内容）

++ date
+ echo 'timestamp: Fri 17 Feb 2023 08:48:01 AM CST'
timestamp: Fri 17 Feb 2023 08:48:01 AM CST
+ echo 'env values:'
env values:
+ printenv
SHELL=/bin/bash
PWD=/root
LOGNAME=root
TEMPDIR=/tmp/user/0
HOME=/root
LANG=en_US.UTF-8
TMPDIR=/tmp/user/0
USER=root
TEMP=/tmp/user/0
SHLVL=2
BASH_ENV=/root/.bashrc
TMP=/tmp/user/0
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
_=/usr/bin/printenv
+ whoami
root
+ cd /
+ echo 'ls -la'
ls -la
+ ls -la
total 60
drwxr-xr-x  18 root root  4096 Feb 17 00:17 .
drwxr-xr-x  18 root root  4096 Feb 17 00:17 ..
lrwxrwxrwx   1 root root     7 Feb  7 19:48 bin -> usr/bin
drwxr-xr-x   4 root root  4096 Feb 12 20:57 boot
drwxr-xr-x   7 root root   400 Feb 16 16:53 dev
drwxr-xr-x  99 root root  4096 Feb 16 17:09 etc
d---------   2 root root    40 Feb 16 16:53 home
lrwxrwxrwx   1 root root    31 Feb  7 19:51 initrd.img -> boot/initrd.img-5.10.0-21-amd64
lrwxrwxrwx   1 root root    31 Feb  7 19:49 initrd.img.old -> boot/initrd.img-5.10.0-20-amd64
lrwxrwxrwx   1 root root     7 Feb  7 19:48 lib -> usr/lib
lrwxrwxrwx   1 root root     9 Feb  7 19:48 lib32 -> usr/lib32
lrwxrwxrwx   1 root root     9 Feb  7 19:48 lib64 -> usr/lib64
lrwxrwxrwx   1 root root    10 Feb  7 19:48 libx32 -> usr/libx32
drwx------   2 root root 16384 Feb  7 19:48 lost+found
drwxr-xr-x   3 root root  4096 Feb  7 19:49 media
drwxr-xr-x   7 root root  4096 Feb 16 20:42 mnt
drwxr-xr-x   2 root root  4096 Feb  7 19:48 opt
dr-xr-xr-x 192 root root     0 Feb 16 16:53 proc
d---------   2 root root    40 Feb 16 16:53 root
drwxr-xr-x  25 root root   800 Feb 17 00:18 run
lrwxrwxrwx   1 root root     8 Feb  7 19:48 sbin -> usr/sbin
drwxr-xr-x   2 root root  4096 Feb  7 19:48 srv
dr-xr-xr-x  13 root root     0 Feb 16 16:53 sys
drwxrwxrwt  11 root root  4096 Feb 17 08:47 tmp
drwxr-xr-x  14 root root  4096 Feb  7 19:48 usr
drwxr-xr-x  12 root root  4096 Feb  7 20:14 var
lrwxrwxrwx   1 root root    28 Feb  7 19:51 vmlinuz -> boot/vmlinuz-5.10.0-21-amd64
lrwxrwxrwx   1 root root    28 Feb  7 19:49 vmlinuz.old -> boot/vmlinuz-5.10.0-20-amd64
+ cd /dev
+ echo 'cd to /dev, then ls -la'
cd to /dev, then ls -la
+ ls -la
total 4
drwxr-xr-x  7 root root  400 Feb 16 16:53 .
drwxr-xr-x 18 root root 4096 Feb 17 00:17 ..
drwxr-xr-x  2 root root  180 Feb 16 16:53 char
lrwxrwxrwx  1 root root   11 Feb 16 16:53 core -> /proc/kcore
lrwxrwxrwx  1 root root   13 Feb 16 16:53 fd -> /proc/self/fd
crw-rw-rw-  1 root root 1, 7 Feb 16 16:53 full
drwxr-xr-x  2 root root    0 Feb 16 16:53 hugepages
lrwxrwxrwx  1 root root   28 Feb 16 16:53 log -> /run/systemd/journal/dev-log
drwxrwxrwt  2 root root   40 Feb 16 16:53 mqueue
crw-rw-rw-  1 root root 1, 3 Feb 16 16:53 null
crw-rw-rw-  1 root root 5, 2 Feb 16 16:53 ptmx
drwxr-xr-x  2 root root    0 Feb 16 16:53 pts
crw-rw-rw-  1 root root 1, 8 Feb 16 16:53 random
drwxrwxrwt  2 root root   40 Feb 17 00:17 shm
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stderr -> /proc/self/fd/2
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stdin -> /proc/self/fd/0
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stdout -> /proc/self/fd/1
crw-rw-rw-  1 root root 5, 0 Feb 16 16:53 tty
crw-rw-rw-  1 root root 1, 9 Feb 16 16:53 urandom
crw-rw-rw-  1 root root 1, 5 Feb 16 16:53 zero
+ cd disk
/usr/local/bin/problem: line 17: cd: disk: No such file or directory
+ echo 'cd to /dev/disk, then ls -la'
cd to /dev/disk, then ls -la
+ ls -la
total 4
drwxr-xr-x  7 root root  400 Feb 16 16:53 .
drwxr-xr-x 18 root root 4096 Feb 17 00:17 ..
drwxr-xr-x  2 root root  180 Feb 16 16:53 char
lrwxrwxrwx  1 root root   11 Feb 16 16:53 core -> /proc/kcore
lrwxrwxrwx  1 root root   13 Feb 16 16:53 fd -> /proc/self/fd
crw-rw-rw-  1 root root 1, 7 Feb 16 16:53 full
drwxr-xr-x  2 root root    0 Feb 16 16:53 hugepages
lrwxrwxrwx  1 root root   28 Feb 16 16:53 log -> /run/systemd/journal/dev-log
drwxrwxrwt  2 root root   40 Feb 16 16:53 mqueue
crw-rw-rw-  1 root root 1, 3 Feb 16 16:53 null
crw-rw-rw-  1 root root 5, 2 Feb 16 16:53 ptmx
drwxr-xr-x  2 root root    0 Feb 16 16:53 pts
crw-rw-rw-  1 root root 1, 8 Feb 16 16:53 random
drwxrwxrwt  2 root root   40 Feb 17 00:17 shm
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stderr -> /proc/self/fd/2
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stdin -> /proc/self/fd/0
lrwxrwxrwx  1 root root   15 Feb 16 16:53 stdout -> /proc/self/fd/1
crw-rw-rw-  1 root root 5, 0 Feb 16 16:53 tty
crw-rw-rw-  1 root root 1, 9 Feb 16 16:53 urandom
crw-rw-rw-  1 root root 1, 5 Feb 16 16:53 zero
+ echo ' '
 
+ echo 'just because someone might ask, try to ls /dev/disk directly from /'
just because someone might ask, try to ls /dev/disk directly from /
+ cd /
+ ls -la /dev/disk
ls: cannot access '/dev/disk': No such file or directory
linux