Bash 可以在执行子进程的同时防止子进程继承文件描述符吗?
if flock -nx 9
then
# If begin program runs away, it will keep the lock.
begin program
else
echo "Lock held :/)" >&2
fi 9> /tmp/lk
答案1
据我所知,没有。您必须手动关闭它:
if flock 9 -nx
then
program 9>&- #<= manual close of fd 9 after `program` has forked but before it execs
else
echo "Lock held :/)" >&2
fi 9> /tmp/lk
fcntl
如果你想获得额外的 hacky,你可以通过直接调用该函数来设置标志ctypes.sh:
#!/bin/bash
echo initial
ls /proc/$$/fd/
echo with 9
{
ls /proc/$$/fd/
echo with 9 in an execced child
bash -c ' ls /proc/$$/fd/'
} 9</etc/passwd
echo
echo BEGIN MAGIC
FD_CLOEXEC=1
FD_SETFD=2
. ctypes.sh
echo initial
ls /proc/$$/fd/
echo with 9
{
dlcall fcntl int:9 int:$FD_SETFD int:$FD_CLOEXEC
ls /proc/$$/fd/
echo with 9 in an execced child
bash -c ' ls /proc/$$/fd/'
} 9</etc/passwd
输出:
initial
0
1
2
255
with 9
0
1
2
255
9
with 9 in an execced child
0
1
2
3
9
BEGIN MAGIC
initial
0
1
2
255
with 9
0
1
2
255
9
with 9 in an execced child
0
1
2
3
(不是粘贴错误——当子bash被执行时,9确实被关闭了)。
答案2
使用 bash 5.0+ 和示例可加载模块(debian 要求您还安装该bash-builtins
软件包),您可以使用 fdflags 可加载模块。
if flock -nx 9
then
enable -f /usr/lib/bash/fdflags fdflags
fdflags -s+cloexec 9
begin program
else
echo "Lock held :/)" >&2
fi 9> /tmp/lk